Light diffusion film and light diffusion film manufacturing method

ABSTRACT

Provided are a light diffusion film having a single-layered light diffusion layer, in which the uniformity of the intensity of diffused light in the light diffusion angle region can be increased, or the light diffusion angle region can be expanded effectively, by regulating the combination of the angles of inclination of pillar-shaped objects in plural columnar structure regions, and a method for manufacturing a light diffusion film. Disclosed is a light diffusion film having a single-layered light diffusion layer, the light diffusion film having a first columnar structure region and a second columnar structure region, in which plural pillar-shaped objects having a relatively high refractive index are arranged to stand close together in a region having a relatively low refractive index, sequentially from the lower part of the film along the film plane.

TECHNICAL FIELD

The present invention relates to a light diffusion film and a method formanufacturing a light diffusion film.

More particularly, the present invention relates to a light diffusionfilm composed of a single layer, which is capable of increasing theuniformity of the intensity of diffused light in the light diffusionangle region, or effectively expanding the light diffusion angle region,by regulating the combination of the angles of inclination ofpillar-shaped objects in plural columnar structure regions, and to amethod for manufacturing a light diffusion film.

BACKGROUND ART

Conventionally, for example, in the field of optical technology to whichliquid crystal display devices and the like belong, it has beensuggested to use a light diffusion film which can diffuse an incidentlight coming from a particular direction into particular directions,while transmitting straight an incident light coming from any otherdirections.

A variety of forms of such a light diffusion film are known; however, inparticular, light diffusion films having, within the films, a louverstructure in which plural plate-shaped regions having differentrefractive indices are alternately arranged in one arbitrary directionalong the film plane, have been widely used (for example, PatentDocument 1).

Namely, Patent Document 1 discloses a method for manufacturing a lightcontrol plate (light diffusion film) which includes a first step ofretaining on a film a resin composition composed of a plurality ofcompounds, each having one or more polymerizable carbon-carbon doublebonds in their molecules and having a refractive index that is differentfrom the refractive indices of the other compounds, irradiating thecomposition with ultraviolet radiation from a specific direction andthereby curing the resin composition; and a second step of retaining theresin composition on the film of the cured product thus obtained,irradiating with ultraviolet radiation from a direction different fromthat of the first step, and thereby curing the resin composition,characterized in that the second step is repeated if necessary.

On the other hand, regarding another type of light diffusion films,light diffusion films having, within the film, a columnar structure inwhich plural pillar-shaped objects having a relatively high refractiveindex are arranged to stand close together in a region having arelatively low refractive index, have been widely used (for example,Patent Documents 2 and 3).

Namely, Patent Document 2 discloses a manufacturing device by which alight control plate (light diffusion film) is formed by opposing alinear light source to a photocurable resin composition film, and, whileeither the photocurable resin composition film or the linear lightsource, or both are being moved, by irradiating the photocurable resincomposition film with light from the linear light source, thereby curingthe composition. The device for manufacturing a light control plate(light diffusion film) is a device in which the axial direction of thelinear light source crosses the moving direction, and in which aplurality of light blocking thin plates opposed to one another areprovided between the photocurable resin and the linear light source at apredetermined interval in a direction almost perpendicular to the movingdirection, in such a fashion that one edge facing the photocurable resincomposition of each of the light blocking thin plates is parallel to themoving direction.

Furthermore, Patent Document 3 discloses a method for manufacturing ananisotropic diffusion medium (light diffusion film), the methodincluding providing a composition containing a photocurable compoundinto a sheet form, irradiating this sheet with parallel light rays froma predetermined direction P to cure the composition, and thereby formingan aggregate of plural rod-shaped cured regions that are extended inparallel to the direction P, within the sheet, characterized in thataggregates of tubular objects that are arranged in parallel to thedirection P are interposed between a linear light source and the sheet,and light irradiation is performed through these tubular objects.

Furthermore, there has been suggested a light diffusion film having boththe louver structure and the columnar structure described above, withinthe film (for example, Patent Document 4).

That is, Patent Document 4 discloses a light diffusion film having afirst structural region for anisotropically diffusing incident light,and a second structural region for isotropically diffusing incidentlight, characterized in that the first structural region is a louverstructure region in which plural plate-shaped regions having differentrefractive indices are arranged alternately in parallel along thedirection of the film plane, and the second structural region is acolumnar structure region in which plural pillar-shaped objects arearranged to stand close together in a medium, with the pluralpillar-shaped objects having a refractive index different from that ofthe medium.

CITATION LIST Patent Document

Patent Document 1: JP 63-309902 A (Claims)

Patent Document 2: JP 2009-173018 A (Claims)

Patent Document 3: JP 2005-292219 A (Claims)

Patent Document 4: JP 2012-141593 A (Claims)

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, the light diffusion film having a louver structure obtainableby the production method of Patent Document 1 has a problem that amongthe components included in incident light, the light diffusion film cansufficiently diffuse those components that are perpendicular to thelouver structure that is extended in any one arbitrary direction alongthe film plane, but it is difficult for the light diffusion film tosufficiently diffuse those components parallel to the direction of thelouver structure.

Therefore, for example, when the light diffusion film is used as a lightcontrol plate for a reflective type liquid crystal display device, asufficient viewing angle may not be obtained with one sheet of lightdiffusion film, and therefore, there is a problem that plural sheets ofthe light diffusion film should be laminated.

Also, since a laminated structure in which plural louver structures aresequentially formed is used, the uniformity of the intensity of diffusedlight in the light diffusion angle region can be increased, or the lightdiffusion angle region can be expanded effectively; however, there is aproblem that not only the production process is complicated, but alsothe film thickness is increased, so that blurring of images is liable tooccur, or delamination is prone to occur.

Furthermore, although this is characteristic of anisotropic lightdiffusion caused by a louver structure, there is also a problem thatsharp switching in the diffusion condition of light occurs between alight diffusion incident angle region and a non-light diffusion incidentangle region.

On the other hand, the light diffusion film having a columnar structurethat is obtainable by the production apparatus of Patent Document 2 orthe production method of Patent Document 3, can isotropically diffuseincident light, unlike the case of Patent Document 1. However, sincethere is a single columnar structure in the film, there is a problemthat the intensity of diffused light within the light diffusion angleregion is liable to become non-uniform, or the light diffusion angleregion is liable to be insufficient.

Therefore, for example, when the light diffusion film is used as a lightcontrol plate for a reflective type liquid crystal display device,expectably, a sufficient viewing angle may not be obtained with onesheet of light diffusion film, and therefore, there is a problem thatplural sheets of light diffusion films should be laminated.

On the other hand, the light diffusion film having both a louverstructure and a columnar structure as described in Patent Document 4,has a problem that sharp switching in the diffusion condition of lightoccurs between a light diffusion incident angle region and a non-lightdiffusion incident angle region.

Therefore, for example, in a case in which the light diffusion film isused as a light control plate for a reflective type liquid crystaldisplay device, there is a problem that when the display device isslowly inclined with respect to incident light, the display undergoessharp switching between light and shade, and a person viewing thedisplay screen may have feelings of discomfort.

Thus, the inventors of the present invention conducted a thoroughinvestigation in view of such circumstances as described above, and theinventors found that when a first columnar structure region and a secondcolumnar structure region are formed in a same film, the uniformity ofthe intensity of diffused light in the light diffusion angle region canbe increased, or the light diffusion angle region can be expandedeffectively, thus completing the present invention.

That is, an object of the present invention is to provide a lightdiffusion film composed of a single layer which is capable of increasingthe uniformity of the intensity of diffused light in the light diffusionangle region, or of effectively expanding the light diffusion angleregion, by regulating the combination of the angles of inclination ofpillar-shaped objects in plural columnar structure regions, and a methodfor manufacturing the light diffusion film.

Means for Solving Problem

According to the present invention, there is provided a light diffusionfilm having a single-layered light diffusion layer that has a firstcolumnar structure region and a second columnar structure region, inwhich plural pillar-shaped objects having a relatively high refractiveindex are arranged to stand close together in a region having arelatively low refractive index, sequentially from the lower part of thefilm along the film thickness direction, and thus the problems describedabove can be solved.

That is, the light diffusion film of the present invention has a firstcolumnar structure region and a second columnar structure region.

Therefore, the light diffusion angle region can be expanded effectivelyby varying the angles of inclination of the pillar-shaped objectsincluded in the respective columnar structure regions.

On the other hand, when the angles of inclination of the pillar-shapedobjects included in the respective columnar structural regions areoverlapped, the contribution to the light diffusion angle region issmall; however, the length of the pillar-shaped objects as a whole inthe film thickness direction is extended stably. Therefore, theuniformity of the intensity of diffused light in the light diffusionangle region can be increased.

Furthermore, since the light diffusion film of the present invention hasa first columnar structure region and a second columnar structure regionin a single layer, the occurrence of delamination can be basicallysuppressed.

Furthermore, on the occasion of configuring the light diffusion film ofthe present invention, it is preferable that the light diffusion filmhas an overlapping columnar structure region in which the upper end ofthe first columnar structure region and the lower end of the secondcolumnar structure region overlap with each other.

When such a configuration is adopted, the generation of scattered lightin a columnar structure-unformed part between the respective columnarstructure regions can be suppressed, and the uniformity of the intensityof diffused light within the light diffusion angle region can be furtherenhanced.

Furthermore, on the occasion of configuring the light diffusion film ofthe present invention, it is preferable that the overlapping columnarstructure region is formed as the tips of any one side of thepillar-shaped objects respectively originating from the first columnarstructure region and the second columnar structure region, are broughtinto contact with the vicinity of the tips of the pillar-shaped objectsoriginating from the columnar structure region of the other side.

When such a configuration is adopted, columnar structures can bearranged efficiently in a limited film thickness, so that the uniformityof the intensity of diffused light in the light diffusion angle regioncan be enhanced, and the light diffusion angle region can be expandedmore effectively.

Furthermore, on the occasion of configuring the light diffusion film ofthe present invention, it is preferable that the thickness of theoverlapping columnar structure region is adjusted to a value within therange of 1 to 40 μm.

When such a configuration is adopted, the generation of scattered lightin the overlapping portion of the first columnar structure region andthe second columnar structure region in the overlapping columnarstructure region can be suppressed, and the uniformity of the intensityof diffused light in the light diffusion angle region can be maintainedmore stably.

Furthermore, on the occasion of configuring the light diffusion film ofthe present invention, it is preferable that the thickness of theoverlapping columnar structure region is adjusted to a value within therange of 0.1% to 10% of the film thickness (100%).

When such a configuration is adopted, the overlapping condition of thefirst columnar structure region and the second columnar structure regionin the overlapping columnar structure region can be adjusted to a moresatisfactory extent. Therefore, the generation of scattered light in theoverlapping portion of the respective columnar structure regions can besuppressed, and the uniformity of the intensity of diffused light in thelight diffusion angle region can be maintained more stably.

Furthermore, on the occasion of configuring the light diffusion film ofthe present invention, it is preferable that the absolute value of thedifference between the angles of inclination of the pillar-shapedobjects respectively originating from the first columnar structureregion and the second columnar structure region in the overlappingcolumnar structure region, is adjusted to a value of 1° or more.

When such a configuration is adopted, the light diffusion angle regioncan be expanded more effectively.

Furthermore, on the occasion of configuring the light diffusion film ofthe present invention, it is preferable that a main component of thepillar-shaped objects in the first columnar structure region and thesecond columnar structure region is a (meth)acrylic acid ester polymercontaining plural aromatic rings, and a main component of the regionhaving a relatively low refractive index is a urethane (meth)acrylate.

When such a configuration is adopted, the first and second columnarstructure regions can be formed in a more well-defined manner.

Furthermore, another aspect of the present invention relates to a methodfor manufacturing a light diffusion film, the method including thefollowing steps (a) to (d):

(a) a step of preparing a composition for light diffusion film;

(b) a step of applying the composition for light diffusion film on aprocess sheet, and forming a coating layer;

(c) a step of subjecting the coating layer to first active energy rayirradiation, forming a first columnar structure region in the lowerportion of the coating layer, and simultaneously leaving a columnarstructure-unformed region in the upper portion of the coating layer; and

(d) a step of subjecting the coating layer to second active energy rayirradiation, and forming a second columnar structure region in thecolumnar structure-unformed region.

That is, when the method for manufacturing a light diffusion film of thepresent invention is used, since a coating layer formed from apredetermined composition for light diffusion film is subjected to firstand second active energy ray irradiation, the combination of the anglesof inclination of pillar-shaped regions in the first and second columnarstructure regions can be regulated easily.

Furthermore, since the first and second columnar structure regions areformed in a single layer, the occurrence of delamination in the lightdiffusion film thus obtained can be basically suppressed.

Furthermore, on the occasion of carrying out the method formanufacturing a light diffusion film of the present invention, it ispreferable that the first active energy ray irradiation is carried outin an oxygen-containing atmosphere, and also, the second active energyray irradiation is carried out in a non-oxygen atmosphere.

When the method is carried out as such, a columnar structure-unformedregion can be formed stably in the upper portion of the coating layer byutilizing the influence of oxygen inhibition, while forming a firstcolumnar structure region efficiently in the lower portion of thecoating layer.

On the other hand, in the columnar structure-unformed region thusobtained, the influence of oxygen inhibition can be suppressed, andthereby the second columnar structure region can be formed efficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a) and 1(b) are diagrams provided to explain an outline of thelight diffusion film having a columnar structure in the film.

FIGS. 2(a) and 2(b) are diagrams provided to explain the incident angledependency, isotropic light diffusion, and the angle of aperture in alight diffusion film having a columnar structure in the film.

FIGS. 3(a) and 3(b) are diagrams provided to explain the incident angledependency and the angle of aperture in the light diffusion film of thepresent invention.

FIGS. 4(a) to 4(c) are diagrams provided to explain embodiments of thelight diffusion film of the present invention.

FIGS. 5(a) to 5(c) are diagrams provided to explain embodiments of thecolumnar structure region.

FIGS. 6(a) to 6(c) are diagrams provided to explain the overlappingcolumnar structure region.

FIGS. 7(a) to 7(c) are diagrams provided to explain an outline of theproduction method of the present invention.

FIGS. 8(a) to 8(d) are diagrams provided to explain the irradiation ofparallel light.

FIG. 9 is a diagram provided to explain the angle of irradiation ofparallel light.

FIGS. 10(a) and 10(b) are a schematic diagram and a photograph of across-section in the light diffusion film of Example 1.

FIGS. 11(a) to 11(q) are diagrams provided to explain the lightdiffusion characteristics of the light diffusion film of Example 1.

FIGS. 12(a) and 12(b) are a schematic diagram and a photograph of across-section of the light diffusion film of Example 2.

FIGS. 13(a) to 13(v) are diagrams provided to explain the lightdiffusion characteristics of the light diffusion film of Example 2.

FIGS. 14(a) and 14(b) are a schematic diagram and a photograph of across-section of the light diffusion film of Example 3.

FIGS. 15(a) to 15(x) are diagrams provided to explain the lightdiffusion characteristics of the light diffusion film of Example 3.

FIGS. 16(a) and 16(b) are a schematic diagram and a photograph of across-section of the light diffusion film of Comparative Example 1.

FIGS. 17(a) to 17(q) are diagrams provided to explain the lightdiffusion characteristics of the light diffusion film of ComparativeExample 1.

FIGS. 18(a) and 18(b) are a schematic diagram and a photograph of across-section of the light diffusion film of Comparative Example 2.

FIGS. 19(a) to 19(p) are diagrams provided to explain the lightdiffusion characteristics of the light diffusion film of ComparativeExample 2.

MODE(S) FOR CARRYING OUT THE INVENTION First Embodiment

A first embodiment of the present invention relates to a light diffusionfilm having a single-layered light diffusion layer including a firstcolumnar structure region and a second columnar structure region, inwhich plural pillar-shaped objects having a relatively high refractiveindex are arranged to stand close together in a region having arelatively low refractive index, sequentially from the lower part of thefilm along the film thickness direction.

Hereinafter, the light diffusion film as the first embodiment of thepresent invention will be explained specifically with appropriatereference to the drawings.

1. Basic Principles of Light Diffusion in Light Diffusion Film

First of all, the basic principles of light diffusion in a lightdiffusion film will be explained using FIGS. 1 and 2.

First, FIG. 1(a) shows a top view (plan view) of a light diffusion film10, and FIG. 1(b) shows a cross-sectional view of the light diffusionfilm 10 in a case in which the light diffusion film 10 shown in FIG.1(a) is cut in a perpendicular direction along the dotted line A-A, andthe cut surface is viewed from the direction indicated by the arrow.

Furthermore, FIG. 2(a) shows an overall view of the light diffusion film10, and FIG. 2(b) shows a cross-sectional view in the case of viewingthe light diffusion film 10 of FIG. 2(a) from the X-direction.

As illustrated in such a plan view of FIG. 1(a), the light diffusionfilm 10 has a columnar structure 13 composed of pillar-shaped objectshaving a relatively high refractive index 12, and a region having arelatively low refractive index 14.

Furthermore, as illustrated in the cross-sectional view of FIG. 1(b), inthe vertical direction of the light diffusion film 10, the pillar-shapedobjects having a relatively high refractive index 12 and the regionhaving a relatively low refractive index 14 respectively have apredetermined width, and are thereby in a state of being alternatelyarranged.

Thereby, as illustrated in FIG. 2(a), it is speculated that when theincident angle is within the light diffusion incident angle region,incident light is diffused by the light diffusion film 10.

That is, as illustrated in FIG. 1(b), it is speculated that when theincident angle of light entering the light diffusion film 10 has a valuein a predetermined angle range from parallel, that is, a value withinthe light diffusion incident angle region, with respect to the boundarysurface 13′ of the columnar structure 13, incident light (52, 54)escapes through the interior of the pillar-shaped objects 12 having arelatively high refractive index in the columnar structure along thefilm thickness direction while changing the direction, and thereby thedirection of propagation of light on the light exit surface side becomesuneven.

As a result, when the incident angle is within the light diffusionincident angle region, incident light is diffused by the light diffusionfilm 10 and becomes diffused light (52′, 54′).

On the other hand, in a case in which the incident angle of lightentering the light diffusion film 10 is shifted away from the lightdiffusion incident angle region, it is speculated that, as illustratedin FIG. 1(b), incident light 56 directly transmitted by the lightdiffusion film 10, without being diffused by the light diffusion film,and becomes transmitted light 56′.

Meanwhile, in the present invention, the term “light diffusion incidentangle region” means, with respect to the light diffusion film, the rangeof angles of incident light corresponding to the emission of a diffusedlight, when the angle of incident light is changed from a point lightsource.

Also, such a “light diffusion incident angle region” is an angle regiondetermined for each light diffusion film, as shown in FIG. 2(a), basedon the difference in refractive index, the angle of inclination and thelike of columnar structures in the light diffusion film.

Owing to the basic principles described above, the light diffusion film10 having a columnar structure 13 can exhibit, for example, incidentangle dependency in transmission and diffusion of light, as illustratedin FIG. 2(a).

Furthermore, as illustrated in FIG. 1 and FIG. 2, a light diffusion filmhaving the columnar structure 13 usually exhibits “isotropy”.

Here, the term “isotropy” as used in the present invention means that,as illustrated in FIG. 2(a), when incident light is diffused by a film,the diffusion condition (shape of diffusion of diffused light) of theemitted light that has been diffused in a plane parallel to the film hasa property of not changing with the direction in the same plane.

More specifically, as illustrated in FIG. 2(a), when incident light isdiffused by the film, the diffusion condition of emitted light that hasbeen diffused is circular in a plane parallel to the film.

Also, as illustrated in FIG. 2(b), when the term “incident angle θ1” ofincident light is used in the present invention, the incident angle θ1means the angle (°) obtainable in a case in which the angle of thenormal line to the incident side surface of the light diffusion film isdesignated as 0°.

Furthermore, in the present invention, the “light diffusion angleregion” means the range of angles of the diffused light obtained byfixing a point light source at an angle for which the incident light isthe most diffused.

Furthermore, according to the present invention, the term “angle ofaperture of diffused light” is the width of angle (°) of the “lightdiffusion angle region” described above, and as illustrated in FIG.2(b), means the angle of aperture of diffused light θ2 in a case inwhich a cross-section of the film is viewed from the direction indicatedby the arrow X.

Meanwhile, it has been recognized that the width of angle (°) of thelight diffusion angle region and the width of the light diffusionincident angle region are approximately equal.

Furthermore, as illustrated in FIG. 2(a), in a light diffusion film,when incident angles of incident light are included in the lightdiffusion incident angle region, even if the incident angles aredifferent, almost the same light diffusion can be achieved in the lightexist surface side.

Therefore, it can be said that the resulting light diffusion film has alight-converging effect of concentrating light into a predeterminedsite.

Meanwhile, regarding the change of direction of incident light in theinterior of pillar-shaped objects 12, the case in which the change ofdirection is of step-index type, with the direction being changed from astraight line form to a zigzag form due to total reflection asillustrated in FIG. 1(b), as well as the case in which the change ofdirection is of gradient-index type, with the direction being changed toa curved from, may be considered.

Furthermore, in FIGS. 1(a) and 1(b), the boundary surface between thepillar-shaped objects having a relatively high refractive index 12 andthe region having a relatively low refractive index 14 is indicated witha straight line for the purpose of simplicity; however, in reality, theinterface is slightly meandering, and each of the pillar-shaped objectsforms a complicated refractive index distribution structure accompaniedby branching or disappearance.

As a result, it is speculated that a non-even distribution of opticalcharacteristics increases light diffusibility.

2. Basic Configuration

Next, the basic configuration of the light diffusion film of the presentinvention will be explained using the drawings.

As illustrated in FIGS. 3(a) and 3(b), the light diffusion film 40 ofthe present invention is characterized by including a first columnarstructure region 20 and a second columnar structure region 30 in thesame film, sequentially from the lower part of the film along the filmthickness direction.

Therefore, in the light diffusion film of the present invention, forexample, as illustrated in FIG. 3(a), the light diffusion angle regionand the light diffusion incident angle region can be expandedeffectively by varying the angles of inclination of the pillar-shapedobjects included in the respective columnar structure regions.

On the other hand, as illustrated in FIG. 3(b), when the angles ofinclination of the pillar-shaped objects included in the respectivecolumnar structure regions are overlapped, the contribution to theexpansion of the light diffusion angle region is small; however, thelength of the pillar-shaped objects as a whole in the film thicknessdirection is extended stably. Therefore, the uniformity of the intensityof diffused light in the light diffusion angle region can be enhancedefficiently.

Meanwhile, the term “lower part” described above means, when a coatinglayer is provided on a process sheet, the side closer to the processsheet in the film thickness direction of the coating layer. Therefore,the term is a term used for convenience in the explanation of thepresent invention, and is not intended to limit the up and downdirections of the light diffusion film itself.

Furthermore, the light diffusion film of the present invention can adoptthe embodiments illustrated in FIGS. 4(a) and 4(b).

That is, a first embodiment is a light diffusion film 40 having, asillustrated in FIG. 4(a), an overlapping columnar structure region 50 inwhich the upper end of a first columnar structure region 20 and thelower end of a second columnar structure region 30 overlap with eachother.

Furthermore, a second embodiment is a light diffusion film 40 in which,as illustrated in FIG. 4(b), at the interface between a first columnarstructure region 20 and a second columnar structure region 30, thereexists a gap portion 50′ where a columnar structure is not formed, orthe first columnar structure region 20 and the second columnar structureregion 30 are in exact contact.

On the other hand, as illustrated in FIG. 4(c), a light diffusion film42 in which two columnar structure regions (20, 30) existing in theinterior of the film are excessively overlapping with each other, is notincluded in the light diffusion film of the present invention.

In this regard, since the light diffusion film of the present inventionis characterized by having two columnar structure regions in the samefilm, it is indeed essential in the production method to carry outactive energy ray irradiation in two stages on a single coating layerformed from a composition for light diffusion film.

It is because in such a production method, the light diffusion film 42illustrated in FIG. 4(c) may not be obtained.

Furthermore, in the light diffusion film 42, since the difference inrefractive index between the pillar-shaped objects and the surroundingareas is extremely small, the effects of the present invention ofincreasing the uniformity of the intensity of diffused light oreffectively expanding the light diffusion angle region may not besufficiently obtained.

3. First Columnar Structure Region

The light diffusion film of the present invention is characterized byhaving a first columnar structure region in which plural pillar-shapedobjects having a relatively high refractive index are arranged to standclose together in a region having a relatively low refractive index.

The first columnar structure region will be specifically explained belowusing the drawings.

Meanwhile, in FIG. 5, in order to simplify the explanation, any one ofthe first columnar structure region or the second columnar structureregion is extracted and presented. Therefore, the expression “20 (30)”in FIG. 5 is meant to represent any one of the first columnar structureregion 20 or the second columnar structure region 30 in FIG. 3.

(1) Refractive Index

In regard to the columnar structure region, it is preferable that thedifference between the refractive index of the pillar-shaped objectshaving a relatively high refractive index and the refractive index ofthe region having a relatively low refractive index is adjusted to avalue of 0.01 or more.

The reason for this is that when such a difference in the refractiveindex is adjusted to a value of 0.01 or more, incident light can bereflected stably within the columnar structure region, and the incidentangle dependency and the angle of aperture of diffused light can befurther enhanced.

That is, it is because if such a difference in the refractive index hasa value of below 0.01, since the angle range in which incident lightundergoes total reflection in the columnar structure region is narrowed,the incident angle dependency may be excessively decreased, or the angleof aperture of diffused light may be excessively narrowed.

Therefore, it is more preferable that the difference between therefractive index of the pillar-shaped objects having a relatively highrefractive index and the refractive index of the region having arelatively low refractive index in the columnar structure region isadjusted to a value of 0.05 or more, and even more preferably to a valueof 0.1 or more.

Meanwhile, it is more preferable if the difference in the refractiveindex is larger; however, from the viewpoint of appropriately selectingthe material capable of forming the columnar structure region, a valueof about 0.3 may be considered as the upper limit.

(2) Maximum Diameter

Furthermore, as illustrated in FIG. 5(a), it is preferable that in thecolumnar structure region, the maximum diameter Sc in a cross-section ofa pillar-shaped object is adjusted to a value within the range of 0.1 to15 μm.

The reason for this is that, when such a maximum diameter is adjusted toa value within the range of 0.1 to 15 μm, incident light can bereflected more stably in the columnar structure region, and the incidentangle dependency and the angle of aperture of diffused light can befurther enhanced.

That is, it is because if such a maximum diameter has a value of below0.1 μm, it may be difficult to exhibit light diffusibility, irrespectiveof the incident angle of incident light. On the other hand, if such amaximum diameter has a value of above 15 μm, the amount of light thatpropagates straight through the columnar structure region increases, andthe uniformity of light diffusion may be deteriorated.

Therefore, in regard to the columnar structure region, it is morepreferable that the maximum diameter in a cross-section of apillar-shaped object is adjusted to a value within the range of 0.5 to10 μm, and even more preferably to a value within the range of 1 to 5μm.

Meanwhile, the cross-sectional shape of the pillar-shaped object is notparticularly limited; however, it is preferable to use, for example, acircular shape, an elliptical shape, a polygonal shape, or an irregularshape.

Also, a cross-section of a pillar-shaped object means a cross-sectionobtained by cutting the pillar-shaped object at a plane parallel to thefilm surface.

Meanwhile, the maximum diameter, length and the like of thepillar-shaped object can be calculated by observing the pillar-shapedobject using an opto-digital microscope.

(3) Thickness

Furthermore, as illustrated in FIG. 5(b), it is preferable that thethickness (length) La of the pillar-shaped objects in the columnarstructure region is adjusted to a value within the range of 30 to 500μm.

The reason for this is that, if such a thickness has a value of below 30μm, because the thickness of the pillar-shape objects is insufficient,the amount of incident light that propagates straight through thecolumnar structure region increases, and it may be difficult to obtainsufficient incident angle dependency and a sufficient angle of apertureof diffused light. On the other hand, it is because, if such a thicknesshas a value of above 500 μm, when the columnar structure region isformed by irradiating a composition for light diffusion film with activeenergy radiation, the direction of progress of photopolymerization isdiffused by the columnar structure initially formed, and it may bedifficult to form a desired columnar structure region.

Therefore, it is more preferable that the thickness of the pillar-shapedobjects in the columnar structure region is adjusted to a value withinthe range of 50 to 300 μm, and even more preferably to a value withinthe range of 70 to 200 μm.

(4) Distance Between Pillar-Shaped Objects

Furthermore, as illustrated in FIG. 5(a), it is preferable that thedistance between pillar-shaped objects, that is, the space P betweenadjacent pillar-shaped objects, in the columnar structure region isadjusted to a value within the range of 0.1 to 15 μm.

The reason for this is that when such a distance is adjusted to a valuewithin the range of 0.1 to 15 μm, incident light can be reflected morestably in the columnar structure region, and the incident angledependency and the angle of aperture of diffused light can be furtherenhanced.

That is, it is because if such a distance has a value of below 0.1 μm,it may be difficult to exhibit light diffusibility irrespective of theincident angle of incident light. On the other hand, it is because ifsuch a distance has a value of above 15 μm, the amount of light thatpropagates straight through the columnar structure region increases, andthe uniformity of light diffusion may be deteriorated.

Therefore, in the columnar structure region, it is more preferable thatthe distance between pillar-shaped objects is adjusted to a value withinthe range of 0.5 to 10 μm, and even more preferably to a value withinthe range of 1 to 5 μm.

(5) Angle of Inclination

Furthermore, as illustrated in FIG. 5(b), it is preferable that in thecolumnar structure region, pillar-shaped objects 12 are arranged tostand close together at a constant angle of inclination θa with respectto the film thickness direction.

The reason for this is that, when the angle of inclination of thepillar-shaped objects is made constant, incident light can be reflectedmore stably in the columnar structure region, and the incident angledependency and the angle of aperture of diffused light can be furtherenhanced.

Furthermore, as illustrated in FIG. 5(c), it is also preferable that thepillar-shaped objects are bent.

The reason for this is that when the pillar-shaped objects are bent, theamount of incident light that propagates straight through the columnarstructure region can be decreased, and the uniformity of light diffusioncan be enhanced.

Meanwhile, such bent pillar-shaped objects can be obtained byirradiating light while changing the angle of irradiation of irradiatedlight when active energy ray irradiation is performed; however, suchbent pillar-shaped objects are also largely dependent on the kind of thematerial that forms the columnar structure region.

Furthermore, θa means the angle of inclination (°) of a pillar-shapedobject in a case in which the angle of the normal line with respect tothe film surface, which is measured at a cross-section obtainable whenthe film is cut by a plane that is a plane perpendicular to the filmplane and cuts one whole pillar-shaped object into two along the axialline is designated as 0° (narrower angle between the angles formed bythe normal line and the pillar-shaped object). Meanwhile, the angle ofinclination in the case in which the pillar-shaped objects are inclinedto the right side as illustrated in FIG. 5(b) is taken as the reference,and the angle of inclination in the case in which the pillar-shapedobjects are inclined to the left side is described with a minus sign.

4. Second Columnar Structure Region

The light diffusion film of the present invention is characterized bhaving a second columnar structure region in which plural-pillar-shapedobjects having a relatively high refractive index are arranged to standclose together in a region having a relatively low refractive index.

Meanwhile, since the configuration of the second columnar structureregion is basically the same as the configuration of the first columnarstructure region, specific details will not be repeated here.

However, from the viewpoint that the second columnar structure regionaccomplishes a role as an auxiliary of the first columnar structureregion in light diffusion, it is preferable that the thickness isadjusted to a value within the range of 10 to 200 μm, more preferably toa value within the range of 20 to 150 μm, and even more preferably to avalue within the range of 40 to 100 μm.

Furthermore, it is preferable that the value obtained by subtracting thethickness of the overlapping columnar structure region that will bedescribed below, from the sum of the thicknesses of the first columnarstructure region and the second columnar structure region, is adjustedto a value of 80% or more relative to the film thickness (100%).

The reason for this is that, when the proportion occupied by the sum ofthe regions in which columnar structures are formed with respect to theentirety of the film is adjusted to a value within such a range, theuniformity of the intensity of diffused light in the light diffusionangle region originating from the first columnar structure region andthe second columnar structure region can be enhanced more effectively.

That is, it is because if the proportion occupied by the sum of theregions in which columnar structures are formed with respect to theentirety of the film has a value of below 80%, the absolute amount ofthe columnar structure is insufficient, and it may be difficult toobtain sufficient uniformity of the intensity of diffused light in thelight diffusion angle region.

On the other hand, since a higher proportion occupied by the sum of theregions in which columnar structures are formed with respect to theentirety of the film, is more preferred, the upper limit is 100%.

However, when stable reproducibility or the like is considered, theupper limit is preferably about 98%.

5. Overlapping Columnar Structure Region

It is preferable that the light diffusion film of the present inventionhas an overlapping columnar structure region in which the upper end of afirst columnar structure region and the lower end of a second columnarstructure region overlap with each other.

The reason for this is that when the light diffusion film has anoverlapping columnar structure region, uniformization of the intensityof diffused light in the light diffusion angle region can be realizedefficiently for a limited film thickness.

Hereinafter, the overlapping columnar structure region will be explainedspecifically.

(1) Configuration

The overlapping columnar structure region 50 is not particularly limitedas long as it is formed by the upper end of the first columnar structureregion 20 and the lower end of the second columnar structure region 30overlapping with each other.

More specifically, as illustrated in FIGS. 6(a) and 6(b), it ispreferable that the overlapping columnar structure region is anoverlapping columnar structure region 50 in which the tip of any one ofthe first columnar structure region 20 and the second columnar structureregion 30 is in contact with the vicinity of the tips of thepillar-shaped objects originating from the other columnar structureregion.

Alternatively, as illustrated in FIG. 6(c), an overlapping columnarstructure region 50 in which the respective pillar-shaped objectsoriginating from the first columnar structure region 20 and the secondcolumnar structure region 30 are overlapping in a non-contact state, isalso preferred.

(2) Different in Angle of Inclination

Furthermore, it is preferable that the absolute value of the differencebetween the angles of inclination of the pillar-shaped objectsrespectively originating from the first columnar structure region andthe second columnar structure region is adjusted to a value of 1° ormore.

That is, as illustrated in FIG. 6(a), it is preferable that the absolutevalue of the difference between the angle of inclination θa of thepillar-shaped objects originating from the first columnar structureregion and the angle of inclination θb′ of the pillar-shaped objectsoriginating from the second columnar structure region is adjusted to avalue of 1° or more.

The reason for this is that the light diffusion angle region can beexpanded more effectively by adjusting the absolute value of such adifference in the angle of inclination to a value of 1° or more.

On the other hand, if the absolute value of such a difference in theangle of inclination has an excessively large value, the diffused lightattributable to the various columnar structure regions of the lightdiffusion film thus obtainable becomes completely independent of eachother, and efficient expansion of the light diffusion angle region maynot be achieved.

Therefore, it is more preferable that the absolute value of thedifference between the angle of inclination θa of the pillar-shapedobjects originating from the first columnar structure region and theangle of inclination θb′ of the pillar-shaped objects, is adjusted to avalue within the range of 2° to 30°, and even more preferably to a valuewithin the range of 5° to 20°.

Meanwhile, θa and θb′ mean the angles of inclination (°) ofpillar-shaped objects when the angle of the normal line with respect tothe film surface, which is measured at a cross-section in a case inwhich the film is cut by a plane that is a plane perpendicular to thefilm plane and cuts one whole pillar-shaped object into two along theaxial line, is designated as 0°.

More specifically, as illustrated in FIGS. 6(a) to 6(c), θa means thenarrower angle between the angles formed by the normal line of the upperend surface of the first columnar structure region and the top of thepillar-shaped objects.

Furthermore, θb′ means the narrower angle between the angles formed bythe normal line of the lower end surface of the second columnarstructure region and the bottom of the pillar-shaped objects.

Also, the angle of inclination in the case in which the pillar-shapedobjects are inclined to the right side as illustrated in FIGS. 6(a) to6(c) is taken as the reference, and the angle of inclination in the casein which the pillar-shaped objects are inclined to the left side isdescribed with a minus sign.

Meanwhile, as illustrated in FIGS. 6(a) to 6(c), θb means the narrowerangle between the angles formed by the normal line of the lower endsurface of the first columnar structure region and the bottom of thepillar-shaped objects, and θa′ means the narrower angle between theangles formed by the normal line of the upper end surface of the secondcolumnar structure region and the top of the pillar-shaped objects.

Furthermore, it is preferable that the absolute value of the angle ofinclination of the pillar-shaped objects originating from the secondcolumnar structure region has a larger value than the absolute value ofthe angle of inclination of pillar-shaped objects having a differentrefractive index, which originate from the first columnar structureregion.

The reason for this is that, when such a configuration is adopted,pillar-shaped objects having a sufficient length along the filmthickness direction can be obtained in the second columnar structureregion that is relatively difficult to form compared to the firstcolumnar structure region, and the light diffusion angle region can beexpanded more effectively.

(3) Thickness

Furthermore, it is preferable that the thickness Lb of the overlappingcolumnar structure region is adjusted to a value within the range of 1to 40 μm.

The reason for this is that, when the thickness Lb of the overlappingcolumnar structure region is adjusted to a value within such a range,the overlapping condition of the first columnar structure region and thesecond columnar structure region in the overlapping columnar structureregion can be adjusted to a suitable range, and therefore, thegeneration of scattered light in the connection part of the respectivecolumnar structure regions can be suppressed, while the uniformity ofthe intensity of diffused light in the light diffusion angle region canbe maintained more stably.

That is, it is because if the thickness Lb of the overlapping columnarstructure region has a value of below of 1 μm, scattered light is easilygenerated in the connection part of the respective columnar structureregions, and it may be difficult to maintain the uniformity of theintensity of diffused light in the light diffusion angle region morestably. On the other hand, it is because if the thickness Lb of theoverlapping columnar structure region has a value of above 40 μm, theextraction efficiency of diffused light may be decreased. That is, ifthe thickness Lb of the overlapping columnar structure region is toolong, backscattering or the like occurs in the relevant region, and thisis expected to cause a decrease in the extraction efficiency of diffusedlight.

Therefore, it is more preferable that the thickness Lb of theoverlapping columnar structure region is adjusted to a value within therange of 3 to 35 μm, and even more preferably to a value within therange of 5 to 30 μm.

Furthermore, it is preferable that the thickness of the overlappingcolumnar structure region is adjusted to a value within the range of0.1% to 10% of the film thickness (100%).

The reason for this is that, when the proportion occupied by theoverlapping columnar structure region in the entirety of the film isadjusted to a value within such a range, the overlapping condition ofthe first columnar structure region and the second columnar structureregion in the overlapping columnar structure region can be adjusted to amore suitable range, and therefore, the generation of scattered light ina columnar structure-unformed portion between the respective columnarstructure regions can be suppressed, while the extraction efficiency oflight diffusion can be maintained more stably.

That is, it is because if the proportion occupied by the overlappingcolumnar structure region in the entire film has a value of below 0.1%,the portion in which the first columnar structure region and the secondcolumnar structure region do not form an overlapping structuremicroscopically may become large. Therefore, scattered light is liableto be generated in the relevant structural region, and the extractionefficiency of diffused light may be decreased. On the other hand, it isbecause if the proportion occupied by the overlapping columnar structureregion in the entire film has a value of above 10%, the thickness of thefirst or second columnar structure region may become relativelyinsufficient.

Therefore, it is more preferable that the thickness of the overlappingcolumnar structure region is adjusted to a value within the range of0.2% to 5%, and even more preferably to a value within the range of 0.5%to 4%, relative to the film thickness (100%).

6. Total Film Thickness

Furthermore, it is preferable that the total film thickness of the lightdiffusion film of the present invention is adjusted to a value withinthe range of 60 to 700 μm.

The reason for this is that, if the total film thickness of the lightdiffusion film has a value of below 60 μm, the amount of incident lightthat propagates straight through the columnar structure regionincreases, and it may be difficult to exhibit light diffusion. On theother hand, it is because if the total film thickness of the lightdiffusion film has a value of above 700 μm, when a columnar structureregion is formed by irradiating a composition for light diffusion filmwith active energy radiation, the direction of progress ofphotopolymerization is diffused by the columnar structure formedinitially, and it may be difficult to form a desired columnar structureregion.

Therefore, it is more preferable that the total film thickness of thelight diffusion film is adjusted to a value within the range of 80 to450 μm, and even more preferably to a value within the range of 100 to250 μm.

Meanwhile, it is also acceptable to provide, for example, a thirdcolumnar structure region, a fourth columnar structural region, and thelike by further alternately forming the first columnar structure regionand the second columnar structure region.

7. Combination of Angles of Inclination

Furthermore, when the light diffusion film of the present invention isused, the light diffusion characteristics can be changed by respectivelyregulating the angles of inclination θa of the pillar-shaped objectswith respect to the film thickness direction in the first columnarstructure region, and the angle of inclination θa′ of the pillar-shapedobjects in the film thickness direction in the second columnar structureregion.

That is, for example, as illustrated in FIG. 3(a), by making theincident angle dependency of the respective columnar structure regionsdifferent, satisfactory incident angle dependency in transmission anddiffusion of light can be realized, and also, the light diffusion angleregion and the light diffusion incident angle region can be expandedeffectively.

In this case, it is preferable that, in the first columnar structureregion, the angle of inclination (θa in FIGS. 6(a) to 6(c)) of thepillar-shaped objects with respect to the film thickness direction isadjusted to a value within the range of −80° to 80°, while in the secondcolumnar structure region, the angle of inclination (θa′ in FIGS. 6(a)to 6(c)) of the pillar-shaped objects with respect to the film thicknessdirection is adjusted to a value within the range of −80° to 80°, andthe absolute value of θa−θa′ is adjusted to a value within the range of0° to 80°. It is more preferable that the absolute value of θa−θa′ isadjusted to a value within the range of 2° to 30°, and even morepreferably to a value within the range of 5° to 20°.

Meanwhile, the term “satisfactory incident angle dependency” means thatthe distinction between the light diffusion incident angle region andthe non-diffusion incident angle region in which incident light isdirectly transmitted without being diffused, is controlled in awell-defined manner.

On the other hand, as illustrated in FIG. 3(b), when the incident angledependency of the respective columnar structure regions is overlapped,the contribution to the expansion of the light diffusion incident angleregion is small; however, since the length of the pillar-shaped objectsas a whole in the film thickness direction is extended stably, theuniformity of the intensity of diffused light within the light diffusionangle region can be expanded effectively.

In this case, it is preferable that, in the first columnar structureregion, the angle of inclination θa of the pillar-shaped objects withrespect to the film thickness direction is adjusted to a value withinthe range of −80° to 80°, while in the second columnar structure region,the angle of inclination θa′ of the pillar-shaped objects with respectto the film thickness direction has a value within the range of −80° to80°, and the absolute value of θa−θa′ is adjusted to a value within therange of 0° to 20°, and it is more preferable that the absolute value ofθa−θa′ is adjusted to a value within the range of 2° to 15°.

Meanwhile, in regard to the light diffusion film of the presentinvention, usually, from the viewpoint of maintaining incident angledependency with regularity, it is preferable that the directions ofinclination of the pillar-shaped objects in the first and secondcolumnar structure regions are the same direction or reverse directionswhen viewed from the above of the film; however, the direction ofinclination is not limited to these depending on the applications.

Furthermore, a blank region in which no columnar structure is formed maybe provided to a predetermined thickness in the lower part of the firstcolumnar structure region and in the upper part of the second columnarstructure region.

8. Adhesive Layer

Furthermore, the light diffusion film obtainable according to theproduction method of the present invention may also additionally includean adhesive layer to be laminated onto an adherend, on one surface orboth surfaces of the light diffusion film.

The adhesive that constitutes such an adhesive layer is not particularlylimited, and any conventionally known acrylic, silicone-based,urethane-based, or rubber-based adhesive can be used.

Second Embodiment

The second embodiment of the present invention relates to a method formanufacturing a light diffusion film characterized by including thefollowing steps (a) to (d):

(a) a step of preparing a composition for light diffusion film;

(b) a step of applying the composition for light diffusion film on aprocess sheet, and forming a coating layer;

(c) a step of subjecting the coating layer to first active energy rayirradiation, forming a first columnar structure region in the lowerportion of the coating layer, and simultaneously leaving a columnarstructure-unformed region in the upper portion of the coating layer; and

(d) a step of subjecting the coating layer to second active energy rayirradiation, and forming a second columnar structure region in thecolumnar structure-unformed region.

Hereinafter, the second embodiment of the present invention will bespecifically explained with reference to the drawings, mainly based onthe differences between the second embodiment and the first embodiment.

1. Step (a): Step of Preparing Composition for Light Diffusion Film

Such step is a step of preparing a predetermined composition for lightdiffusion film.

More specifically, it is a step of mixing at least two polymerizablecompounds having different refractive indices, a photopolymerizableinitiator and, if desired, other additives.

Furthermore, when mixing, the mixture may be stirred at room temperaturebut, from the viewpoint of improving uniformity, for example, it ispreferable to stir the mixture under heating conditions at 40° C. to 80°C. to obtain a uniform liquid mixture.

Furthermore, in order to attain a desired viscosity suitable forcoating, it is also preferable to further add a diluent solvent.

Hereinafter, the composition for light diffusion film will be explainedmore specifically.

(1) High-Refractive Index Polymerizable Compound

(1)-1 Kind

Between the two polymerizable compounds having different refractiveindices, the type of polymerizable compound with comparatively highrefractive index (hereinafter, may be referred to as component (A)) isnot particularly limited, but it is preferable to use a (meth)acrylicester containing a plurality of aromatic rings as main component for thepolymerizable compound.

The reason for this is presumed to be that, when a particular(meth)acrylic ester is incorporated as the component (A), thepolymerization rate of the component (A) can be made faster than thepolymerization rate of the polymerizable compound having a lowerrefractive index (hereinafter, may be referred to as component (B)), soas to induce a predetermined difference between the polymerization ratesof these components, and thus copolymerizability of the two componentscan be effectively decreased.

As a result, when the composition is photocured, a columnar structureregion formed by arranging plural pillar-shaped objects originating fromthe component (A) and having a relatively high refractive index, tostand close together in a region originating from the component (B) andhaving a relatively low refractive index, can be formed efficiently.

Furthermore, it is speculated that when the composition includes aparticular (meth)acrylic acid ester as the component (A), the component(A) has sufficient compatibility with the component (B) in the stage ofexisting as a monomer, while having the compatibility with the component(B) decreased to a predetermined range in the stage of existing asplural monomer molecules connected in the course of polymerization, andthe columnar structure region can be formed more efficiently.

Furthermore, when the composition includes a particular (meth)acrylicacid ester as the component (A), the refractive index of the regionsoriginating from the component (A) in the columnar structure region canbe increased, and the difference in the refractive index between theregions originating from the component (A) and the regions originatingfrom the component (B) can be regulated to a value more than or equal toa predetermined value.

Therefore, when the composition for light diffusion film includes aparticular (meth)acrylic acid ester as the component (A), a columnarstructure region in which plural pillar-shaped objects having arelatively high refractive index are arranged to stand close together ina region having a relatively low refractive index can be obtainedefficiently, together with the characteristics of the component (B) thatwill be described below.

Meanwhile, the term “(meth)acrylic ester containing a plurality ofaromatic rings” means a compound having a plurality of aromatic rings inthe ester residue moiety of the (meth)acrylic ester.

Furthermore, “(meth)acrylic” means both acrylic and methacrylic.

Furthermore, examples of a (meth)acrylic ester containing pluralaromatic compounds as such a component (A) include biphenyl(meth)acrylate, naphthyl (meth)acrylate, anthracyl (meth)acrylate,benzylphenyl (meth)acrylate, biphenyloxyalkyl (meth)acrylate,naphthyloxyalkyl (meth)acrylate, anthracyloxyalkyl (meth)acrylate,benzylphenyloxyalkyl (meth)acrylate and the like, or compounds in whichsome of hydrogen atoms on the aromatic ring have been substituted byhalogen, alkyl, alkoxy, halogenated alkyl, or the like.

Furthermore, as the (meth)acrylic ester containing a plurality ofaromatic rings as the component (A), it is preferable for thecomposition for light diffusion film to contain a compound containing abiphenyl ring, and it is particularly preferable for the composition tocontain a biphenyl compound represented by the following Formula (1):

wherein, in Formula (1), R¹ to R¹⁰ are respectively independent of eachanother; at least one of R¹ to R¹⁰ is a substituent represented by thefollowing Formula (2); and the rest of the substituents represents anyone substituent selected from a hydrogen atom, a hydroxyl group, acarboxyl group, an alkyl group, an alkoxy group, a halogenated alkylgroup, a hydroxyalkyl group, a carboxyalkyl group, and a halogen atom.

wherein in Formula (2), R¹¹ represents a hydrogen atom or a methylgroup; the number of carbon atoms n represents an integer from 1 to 4;and the number of repetitions m represents an integer from 1 to 10.

The reason for this is presumed to be that, when a biphenyl compoundhaving a particular structure is incorporated as the component (A), apredetermined difference between the polymerization rates of thecomponent (A) and the component (B) is induced, and the compatibilitybetween the component (A) and the component (B) can be decreased to apredetermined extent, so that copolymerizability between the twocomponents can be decreased.

Furthermore, the refractive index of the regions originating from thecomponent (A) in the columnar structure region can be increased, and thedifference between the refractive index of the regions originating fromthe component (A) and the refractive index of the regions originatingfrom the component (B) can be more easily regulated to a value more thanor equal to a predetermined value.

Furthermore, when R¹ to R¹⁰ in Formula (1) includes any one of an alkylgroup, an alkoxy group, a halogenated alkyl group, a hydroxyalkyl groupand a carboxyalkyl group, it is preferable to adjust the number ofcarbon atoms of the alkyl moiety to a value within the range of 1 to 4.

The reason for this is that, if such a number of carbon atoms has avalue of above 4, the polymerization rate of the component (A) may bedecreased, or the refractive index of the regions originating from thecomponent (A) may be excessively lowered, and it may be difficult toform the columnar structure region efficiently.

Therefore, when R¹ to R¹⁰ in Formula (1) includes any one of an alkylgroup, an alkoxy group, a halogenated alkyl group, a hydroxyalkyl groupand a carboxyalkyl group, it is more preferable to adjust the number ofcarbon atoms of the alkyl moiety to a value within the range of 1 to 3,and even more preferably to a value within the range of 1 to 2.

Furthermore, it is preferable that R¹ to R¹⁰ in Formula (1) eachrepresent a substituent other than a halogenated alkyl group or ahalogen atom, that is, a substituent that does not contain halogen.

The reason for this is that when the light diffusion film is incineratedor the like, generation of dioxin is prevented, and it is preferablefrom the viewpoint of environmental protection.

Meanwhile, in regard to the conventional light diffusion films having acolumnar structure, it has been general to subject the monomercomponents to halogen substitution for the purpose of increasing therefractive index of the monomer components, on the occasion of obtaininga predetermined columnar structure.

In this regard, when a biphenyl compound represented by Formula (1) isused, even if halogen substitution is not performed, a high refractiveindex can be obtained.

Therefore, if a light diffusion film formed by photocuring thecomposition for light diffusion film according to the present inventionis used, it can exhibit satisfactory incident angle dependency, evenwithout a compound containing halogen.

Furthermore, it is preferable that any one of R² to R⁹ in Formula (1) bea substituent represented by Formula (2).

The reason for this is that, when the position of the substituentrepresented by Formula (2) is set to a position other than the positionof R¹ and the position of R¹⁰, the molecules of the component (A) can beeffectively prevented from aligning and crystallizing in a stage priorto photocuring.

Furthermore, the compound is liquid at the monomer stage prior tophotocuring, and the compound can be apparently uniformly mixed with thecomponent (B) even if a diluent solvent or the like is not used.

It is because thereby, aggregation and phase separation at a fine levelof the component (A) and the component (B) are enabled in the stage ofphotocuring, and a light diffusion film having a columnar structureregion can be obtained more efficiently.

Furthermore, from the same viewpoint, it is particularly preferable thatany one of R³, R⁵, R⁶ and R⁸ in Formula (1) be a substituent representedby Formula (2).

Furthermore, it is usually preferable that the number of repetitions min the substituent represented by Formula (2) be defined as an integerfrom 1 to 10.

The reason for this is that, if the number of repetitions m has a valueexceeding 10, the oxyalkylene chain that links the polymerization siteand the biphenyl ring becomes too long, and polymerization of themolecules of the component (A) at the polymerization site may thereby beinhibited.

Therefore, it is more preferable that the number of repetitions m forthe substituent represented by Formula (2) be defined as an integer from1 to 4, and particularly preferable that it be defined as an integerfrom 1 to 2.

Meanwhile, from the same viewpoint, it is usually preferable that thenumber of carbon atoms n for the substituent represented by Formula (2)be defined as an integer from 1 to 4.

Furthermore, upon considering the case in which the position of apolymerizable carbon-carbon double bond serving as a polymerization siteis so close to the biphenyl ring that the biphenyl ring imposes sterichindrance, and the polymerization rate of the component (A) isdecreased, it is more preferable that the number of carbon atoms n forthe substituent represented by Formula (2) be defined as an integer from2 to 4, and particularly preferable that it be defined as an integerfrom 2 to 3.

Furthermore, specific preferred examples of the biphenyl compoundrepresented by Formula (1) include compounds represented by thefollowing formulas (3) and (4):

(1)-2 Molecular Weight

Furthermore, it is preferable to adjust the molecular weight of thecomponent (A) to a value within the range of 200 to 2,500.

The reason for this is that, by adjusting the molecular weight of thecomponent (A) to a value in a predetermined range, it is presumed thatthe polymerization rate of the component (A) can be made faster, andcopolymerizability of the component (A) and the component (B) can bedecreased more effectively.

As a result, when the composition is photocured, a columnar structureregion in which plural pillar-shaped objects originating from thecomponent (A) and having a relatively high refractive index are arrangedto stand close together in a region originating from the component (B)and having a relatively low refractive index, can be formed moreefficiently.

That is, it is because, if the molecular weight of the component (A) hasa value of below 200, the polymerization rate is decreased by sterichindrance and becomes closer to the polymerization rate of the component(B), and copolymerization with the component (B) is likely to occur. Onthe other hand, it is speculated that if the molecular weight of thecomponent (A) has a value of above 2,500, in addition to the differencein the molecular weight between the component (A) and the component (B)becoming smaller, the polymerization rate of the component (A) isdecreased and becomes closer to the polymerization rate of the component(B), and copolymerization with the component (B) is likely to occur. Asa result, it may be difficult to form a columnar structure regionefficiently.

Therefore, it is more preferable to adjust the molecular weight of thecomponent (A) to a value within the range of 240 to 1,500, and even morepreferably to a value within the range of 260 to 1,000.

Meanwhile, the molecular weight of the component (A) can be determinedfrom the calculated value obtainable from the composition of themolecules and the atomic weight of the constituent atoms, or can bemeasured as the weight average molecular weight using gel permeationchromatography (GPC).

(1)-3 Single Use

Furthermore, the composition for light diffusion film according to thepresent invention is characterized by including the component (A) as amonomer component that forms a region having a relatively highrefractive index in the columnar structure region; however, it ispreferable that the component (A) is included as a single component.

The reason for this is that, when such a configuration is adopted, thefluctuation in the refractive index of the region originating from thecomponent (A), that is, the pillar-shaped objects having a relativelyhigh refractive index, can be suppressed effectively, and thereby, alight diffusion film having a columnar structure region can be obtainedmore efficiently.

That is, when the compatibility of the component (A) with the component(B) is low, for example, when the component (A) is a halogen-basedcompound or the like, another component (A) (for example, anon-halogen-based compound) may be used jointly as a third component formaking the component (A) compatible with the component (B).

However, in that case, the refractive index in the region withcomparatively high refractive index, originating from the component (A),may fluctuate or may become prone to decrease, due to the influence ofsuch a third component.

As a result, the difference in refractive index with the region withcomparatively low refractive index, originating from the component (B),may become non-uniform, or may be prone to decrease excessively.

Therefore, it is preferable to select a high refractive index monomercomponent having compatibility with the component (B), and use thatmonomer component as a single component (A).

Meanwhile, for example, since a biphenyl compound represented by Formula(3) as the component (A) has a low viscosity, the biphenyl compound canbe used as a single component (A) in order to have compatibility withthe component (B).

(1)-4 Refractive Index

Furthermore, it is preferable that the refractive index of the component(A) is adjusted to a value within the range of 1.5 to 1.65.

The reason for this is that when the refractive index of the component(A) has a value within such a range, the difference between therefractive index of the region originating from the component (A) andthe refractive index originating from the component (B) can be regulatedmore easily, and thereby a light diffusion film having a columnarstructure region can be obtained more efficiently.

That is, if the refractive index of the component (A) has a value ofbelow 1.5, the difference between the refractive index of the component(A) and the refractive index of the component (B) becomes too small, andit may be difficult to obtain an effective light diffusion angle region.On the other hand, if the refractive index of the component (A) has avalue exceeding 1.65, the difference between the refractive index of thecomponent (A) and the refractive index of the component (B) becomeslarge, but it may be difficult to even form an apparent compatibilitywith the component (B).

Therefore, it is more preferable to adjust the refractive index of thecomponent (A) to a value within the range of 1.52 to 1.62 and even morepreferable to a value within the range of 1.56 to 1.6.

Meanwhile, the refractive index of the component (A) means therefractive index of the component (A) prior to photocuring.

Furthermore, the refractive index can be measured according to JISK0062.

(1)-5 Content

Furthermore, it is preferable to adjust the amount of component (A) inthe composition for light diffusion film to a value within the range of25 parts to 400 parts by weight relative to 100 parts by weight of thecomponent (B), which is a polymerizable compound with relatively lowrefractive index that will be described hereinafter.

The reason for this is that, if the content of the component (A) has avalue of below 25 parts by weight, the existence ratio of the component(A) to the component (B) is small, the width of the pillar-shapedobjects originating from the component (A) becomes excessively small,and it may be difficult to obtain a columnar structure region havingsatisfactory incident angle dependency. Furthermore, it is because thelength of the pillar-shaped objects in the thickness direction of thelight diffusion film becomes insufficient, and light diffusibility maynot be manifested. On the other hand, it is because if the content ofthe component (A) has a value of above 400 parts by weight, theexistence ratio of the component (A) to the component (B) is increased,the width of the pillar-shaped objects originating from the component(A) becomes excessively large, and in contrast, it may be difficult toobtain a columnar structure region having satisfactory incident angledependency. Furthermore, it is because the length of the pillar-shapedobjects in the thickness direction of the light diffusion film becomesinsufficient, and light diffusibility may not be manifested.

Therefore, it is more preferable to adjust the amount of component (A)to a value within the range of 40 parts to 300 parts by weight, and evenmore preferably to a value within the range of 50 parts to 200 parts byweight, relative to 100 parts by weight of the component (B).

(2) Low-Refractive Index Polymerizable Compound

(2)-1 Kind

Between the two polymerizable compounds having different refractiveindices, the type of the polymerizable compound with comparatively lowrefractive index (component (B)) is not particularly limited, andexamples of main component thereof include urethane (meth)acrylate, a(meth)acrylic polymer having a (meth)acryloyl group in a side chain, a(meth)acryloyl group-containing silicone resin, and an unsaturatedpolyester resin. However, as main component, it is particularlypreferable to use urethane (meth)acrylate.

The reason for this is that when a urethane (meth)acrylate is used, thedifference between the refractive index of the regions originating fromthe component (A) and the refractive index of the regions originatingfrom the component (B) can be regulated more easily, the fluctuation inthe refractive index of the regions originating from the component (B)can be suppressed effectively, and a light diffusion film having acolumnar structure region can be obtained more efficiently.

Therefore, in the following, for the component (B), urethane(meth)acrylate will mainly be described.

Meanwhile, (meth)acrylate means both acrylate and methacrylate.

First, urethane (meth)acrylate is formed from (B1) a compound containingat least two isocyanate groups; (B2) a polyol compound, preferably adiol compound, and particularly preferably polyalkylene glycol; and (B3)hydroxyalkyl (meth)acrylate.

Meanwhile, the component (B) is intended to include an oligomer having arepeating unit of urethane bond.

Among these, examples for the component (B1), the compound containing atleast two isocyanate groups, include aromatic polyisocyanates such as2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylenediisocyanate, and 1,4-xylylene diisocyanate; aliphatic polyisocyanatessuch as hexamethylene diisocyanate; alicyclic polyisocyanates such asisophorone diisocyanate (IPDI) and hydrogenated diphenylmethanediisocyanate; biuret forms and isocyanurate forms thereof; and adductsthat are reaction products with low molecular weight activehydrogen-containing compounds and the like such as ethylene glycol,propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil(for example, xylylene diisocyanate-based trifunctional adduct).

Furthermore, among the compounds described above, it is particularlypreferable to have an alicyclic polyisocyanate.

The reason for this is that alicyclic polyisocyanates are likely toprovide differences in the reaction rates of the various isocyanategroups in relation to the conformation or the like, as compared withaliphatic polyisocyanates.

Thereby, the reactions of the component (B1) with only the component(B2), or the component (B1) with only the component (B3) can beinhibited, and the component (B1) can react reliably with the component(B2) and the component (B3), so that generation of excess byproducts canbe prevented.

As a result, the fluctuation in the refractive index in the regionsoriginating from the component (B), that is, the low-refractive indexregions, in the columnar structure region can be suppressed effectively.

Furthermore, when an alicyclic polyisocyanate is used, the compatibilitybetween the component (B) and the component (A) thus obtainable can bedecreased to a predetermined range, and a columnar structure region canbe formed more efficiently, compared to an aromatic polyisocyanate.

Furthermore, with an alicyclic polyisocyanate, since the refractiveindex of the component (B) thus obtainable can be made smaller comparedto an aromatic polyisocyanate, the difference between the refractiveindex of the component (B) and the refractive index of the component (A)can be made larger, light diffusibility can be manifested more reliably,and also, a columnar structure region having high uniformity of diffusedlight within the light diffusion angle region can be formed moreefficiently.

Furthermore, among such alicyclic polyisocyanates, an alicyclicdiisocyanate containing only two isocyanate groups is preferred.

The reason for this is that when an alicyclic diisocyanate is used, thecomponent (B2) and the component (B3) react quantitatively, and a singlecomponent (B) can be obtained.

Particularly preferred examples of such an alicyclic diisocyanateinclude isophorone diisocyanate (IPDI).

The reason for this is that a significant difference can be provided inthe reactivity of two isocyanate groups.

Furthermore, among the components forming urethane (meth)acrylate, forthe component (B2), examples of polyalkylene glycol include polyethyleneglycol, polypropylene glycol, polybutylene glycol, and polyhexyleneglycol and the like, and among them, polypropylene glycol isparticularly preferred.

The reason for this is that, since a urethane (meth)acrylate derivedfrom polypropylene glycol has low viscosity, the urethane (meth)acrylatecan be handled in a solventless manner.

Furthermore, with polypropylene glycol, when the component (B) is cured,the polypropylene glycol forms a satisfactory soft segment in the curedproduct, and handling ability or decorativeness of the light diffusionfilm can be enhanced effectively.

Meanwhile, the weight average molecular weight of the component (B) canbe adjusted mainly by the weight average molecular weight of thecomponent (B2). Here, the weight average molecular weight of thecomponent (B2) is usually 2,300 to 19,500, preferably 4,300 to 14,300,and particularly preferably 6,300 to 12,300.

Furthermore, among the components forming urethane (meth)acrylate, forthe component (B3), examples of hydroxyalkyl (meth)acrylate include2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate,3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate and thelike.

Furthermore, from the viewpoint of decreasing the obtainablepolymerization rate of the urethane (meth)acrylate and forming apredetermined columnar structure more efficiently, particularly ahydroxyalkyl methacrylate is more preferred, and 2-hydroxyethylmethacrylate is even more preferred.

Furthermore, synthesis of the urethane (meth)acrylate based on thecomponents (B1) to (B3) can be carried out by a conventional method.

In this case, it is preferable to adjust the mixing ratio of thecomponents (B1) to (B3) to a mole ratio of component (B1):component(B2):component (B3)=1 to 5:1:1 to 5.

The reason for this is that, with such a mixing ratio, a urethane(meth)acrylate can be efficiently synthesized, in which each one of theisocyanate groups carried by the components (B1) has reacted with thetwo hydroxyl groups carried by the component (B2) and bonded thereto,and the hydroxyl groups carried by the component (B3) have reacted withthe other isocyanate group respectively carried by the two components(B1) and bonded thereto.

Therefore, it is more preferable to adjust the mixing ratio of thecomponents (B1) to (B3) to a molar ratio of component (B1):component(B2):component (B3)=1 to 3:1:1 to 3, and even more preferably to theratio of 2:1:2.

(2)-2 Weight Average Molecular Weight

Furthermore, it is preferable to adjust the weight average molecularweight of the component (B) to a value within the range of 3,000 to20,000.

The reason for this is that, by adjusting the weight average molecularweight of the component (B) to a predetermined range, a predetermineddifference is caused between the polymerization rates of the component(A) and the component (B), and thus copolymerizability of the twocomponents can be effectively decreased.

As a result, when the composition is photocured, a columnar structureregion in which plural pillar-shaped objects originating from thecomponent (A) and having a relatively high refractive index are arrangedto stand close together in a region originating from the component (B)and having a relatively low refractive index, can be formed efficiently.

That is, it is because, if the weight average molecular weight of thecomponent (B) has a value of below 3,000, the polymerization rate of thecomponent (B) is increased to become closer to the polymerization rateof the component (A), and copolymerization with the component (A) islikely to occur, so that as a result, it may be difficult to form acolumnar structure region efficiently. On the other hand, it is because,if the weight average molecular weight of the component (B) has a valueof above 20,000, it may be difficult to form a columnar structure regionin which plural pillar-shaped objects derived from the component (A) andhaving a relatively high refractive index are arranged to stand closetogether in a region derived from the component (B) and having arelatively low refractive index, or the compatibility with the component(A) is excessively decreased, so that the component (A) may beprecipitated out or the like in the stage of application.

Therefore, it is more preferable to adjust the weight average molecularweight of the component (B) to a value within the range of 5,000 to15,000, and even more preferable to adjust it to a value within therange of 7,000 to 13,000.

Meanwhile, the weight average molecular weight of the component (B) canbe measured using gel permeation chromatography (GPC).

(2)-3 Single Use

Furthermore, regarding the component (B), two or more kinds havingdifferent molecular structures or weight average molecular weights maybe used in combination; however, from the viewpoint of suppressing thefluctuation in the refractive index of the regions originating from thecomponent (B) in the columnar structure region, it is preferable to useonly one kind.

That is, it is because when a plurality of compounds are used for thecomponent (B), the refractive index for the region with comparativelylow refractive index originating from the component (B) may fluctuate orincrease, and the difference of refractive index with the region withcomparatively high refractive index originating from the component (A)may become non-uniform or decrease excessively.

(2)-4 Refractive Index

Furthermore, it is preferable that the refractive index of the component(B) is adjusted to a value within the range of 1.4 to 1.55.

The reason for this is that, when the refractive index of the component(B) is adjusted to a value within such a range, the difference betweenthe refractive index of the regions originating from the component (A)and the refractive index of the regions originating from the component(B) can be regulated more easily, and a light diffusion film having acolumnar structure region can be obtained more efficiently.

That is, it is because, if the refractive index of the component (B) hasa value of below 1.4, the difference between the refractive index of thecomponent (B) and the refractive index of the component (A) becomeslarge; however, compatibility with the component (A) is extremelydeteriorated, and there is a risk that a columnar structure region maynot be formed. On the other hand, it is because if the refractive indexof the component (B) has a value of above 1.55, the difference betweenthe refractive index of the component (B) and the refractive index ofthe component (A) becomes excessively small, and it may be difficult toobtain desired incident angle dependency.

Therefore, it is more preferable to adjust the refractive index of thecomponent (B) to a value within the range of 1.45 to 1.54, and even morepreferably to a value within the range of 1.46 to 1.52.

Meanwhile, the refractive index of the component (B) described abovemeans the refractive index of the component (B) prior to photocuring.

The refractive index can be measured, for example, according to JISK0062.

Furthermore, it is preferable to adjust the difference between therefractive indices of the component (A) and the component (B) to a valueof 0.01 or more.

The reason for this is that, when such difference in refractive index isadjusted to a value in a predetermined range, a light diffusion film canbe obtained, which has more satisfactory incident angle dependency inconnection with the transmission and the diffusion of light, and has abroader light diffusion incident angle region.

That is, it is because, if such a difference in the refractive index hasa value of below 0.01, the angle range for total reflection of theincident light in the columnar structure region is narrowed, and theangle of aperture in light diffusion may be excessively narrowed. On theother hand, it is because, if such a difference in the refractive indexhas an excessively large value, compatibility between the component (A)and the component (B) is excessively deteriorated, and there is a riskthat a columnar structure region may not be formed.

Therefore, it is more preferable to adjust the difference between therefractive indices of the component (A) and the component (B) to a valuewithin the range of 0.05 to 0.5, and even more preferable to adjust itto a value within the range of 0.1 to 0.2.

Meanwhile, the refractive indices of the component (A) and the component(B) mean the refractive indices of the component (A) and the component(B) prior to photocuring.

(2)-5 Content

Furthermore, it is preferable that the content of the component (B) inthe composition for light diffusion film is adjusted to a value withinthe range of 10 parts to 80 parts by weight relative to 100 parts byweight of the total amount of the composition for light diffusion film.

The reason for this is that, if the content of the component (B) has avalue of below 10 parts by weight, the existence ratio of the component(B) to the component (A) becomes small, the regions originating from thecomponent (B) become excessively small compared to the regionsoriginating from the component (A), and it may be difficult to obtain acolumnar structure region having satisfactory incident angle dependency.On the other hand, it is because, if the content of the component (B)has a value of above 80 parts by weight, the existence ratio of thecomponent (B) to the component (A) is increased, the regions originatingfrom the component (B) become excessively large compared to the regionsoriginating from the component (A), and in contrast, it may be difficultto obtain a columnar structure region having satisfactory incident angledependency.

Therefore, it is more preferable that the content of the component (B)is adjusted to a value within the range of 20 parts to 70 parts byweight, and even more preferably to a value within the range of 30 partsto 60 parts by weight, relative to 100 parts by weight of the totalamount of the composition for light diffusion film.

(3) Photopolymerization Initiator

Furthermore, in the composition for light diffusion film according tothe present invention, if desired, it is preferable to incorporate aphotopolymerization initiator as a component (C).

The reason for this is that by incorporating a photopolymerizationinitiator, a columnar structure region can be formed efficiently whenthe composition for light diffusion film is irradiated with activeenergy radiation.

Here, a photopolymerization initiator refers to a compound whichgenerates radical species when irradiated with active energy radiationsuch as ultraviolet radiation.

Examples of such a photopolymerization initiator include benzoin,benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether,benzoin n-butyl ether, benzoin isobutyl ether, acetophenone,dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenylketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,4-(2-hydroxyethoxy)phenyl 2-(hydroxy-2-propyl) ketone, benzophenone,p-phenylbenzophenone, 4,4-diethylaminobenzophenone,dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone,2-tertiary-butylanthraquinone, 2-aminoanthraquinone,2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethylketal, acetophenone dimethyl ketal, p-dimethylamine benzoic acid ester,and oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propane]. Amongthese, one type of compound may be used alone, or two or more types ofcompounds may be used in combination.

Meanwhile, when a photopolymerization initiator is incorporated, it ispreferable to adjust the amount of photopolymerization initiator to avalue within the range of 0.2 parts to 20 parts by weight, morepreferable to adjust it to a value within the range of 0.5 parts to 15parts by weight, and even more preferable to adjust it to a value withinthe range of 1 part to 10 parts by weight, relative to 100 parts byweight of the total amount of the component (A) and the component (B).

(4) Other Additives

Furthermore, additives other than the compounds described above can beappropriately added to the extent that the effect of the presentinvention is not impaired.

Examples of such additives include an oxidation inhibitor, anultraviolet absorber, an antistatic agent, a polymerization accelerator,a polymerization inhibitor, an infrared absorber, a plasticizer, adiluent solvent, a leveling agent, and the like.

Meanwhile, it is generally preferable to adjust the amount of suchadditives to a value within the range of 0.01 parts to 5 parts byweight, more preferable to adjust it to a value within the range of 0.02parts to 3 parts by weight, and even more preferable to adjust it to avalue within the range of 0.05 parts to 2 parts by weight, relative to100 parts by weight of the total amount of the component (A) and thecomponent (B).

2. Step (b): Application Step

Step (b) is a step of applying the composition for light diffusion filmon a process sheet 2, and forming a coating layer 1, as illustrated inFIG. 7(a).

Regarding the process sheet, a plastic film and paper can all be used.

Among these, examples of plastic films include polyester-based filmssuch as a polyethylene terephthalate film; polyolefin-based films suchas a polyethylene film and a polypropylene film, cellulose-based filmssuch as a triacetyl cellulose film, polyimide-based films, and the like.

Furthermore, examples of paper include glassine paper, coated paper, andlaminate paper.

Furthermore, in consideration of the processes that will be describedbelow, the process sheet 2 is preferably a plastic film that hasexcellent dimensional stability against heat or active energy radiation.

Preferred examples of such film include, among those described above, apolyester-based film, a polyolefin-based film, and a polyimide-basedfilm.

Furthermore, in the process sheet, it is preferable to provide a releaselayer on the side of the surface coated with the composition for lightdiffusion film in the process sheet, in order to facilitate peeling ofthe light diffusion film obtained after photocuring from the processsheet.

Such a release layer can be formed using a conventionally known releaseagent such as a silicone-based release agent, a fluorine-based releaseagent, an alkyd-based release agent, an olefin-based release agent orthe like.

Meanwhile, usually, the thickness of the process sheet is preferablyadjusted to a value within the range of 25 μm to 200 μm.

Furthermore, the method of applying a composition for light diffusionfilm on a process sheet can be carried out by, for example, aconventionally known method such as a knife coating method, a rollcoating method, a bar coating method, a blade coating method, a diecoating method, or a gravure coating method.

Meanwhile, at this time, it is preferable that the film thickness of thecoating layer is adjusted to a value within the range of 60 to 700 μm.

3. Step (c): First Active Energy Ray Irradiation Step

Step (c) is, as illustrated in FIG. 7(b), a step of subjecting thecoating layer 1 to first active energy ray irradiation, and forming afirst columnar structure region 20 in the lower portion of the coatinglayer 1, while leaving a columnar structure-unformed region 20′ in theupper portion of the coating layer 1.

That is, in the first active energy ray irradiation step, parallel lightwith high parallelism of light rays is irradiated to the coating layerformed on the process sheet.

Here, parallel light means a light in which the direction of emittedlight is approximately parallel without any spreading when viewed fromany direction.

More specifically, for example, as illustrated in FIG. 8(a), it ispreferable that irradiated light 60 coming from a point light source 202is converted to parallel light 70 by means of a lens 204, and then theparallel light is irradiated to the coating layer, or as illustrated inFIGS. 8(b) and 8(c), irradiated light 60 coming from a linear lightsource 125 is converted to parallel light 70 by means of irradiatedlight parallelizing members 200 (200 a, 200 b), and then the parallellight is irradiated to the coating layer.

Meanwhile, as illustrated in FIG. 8(d), the irradiated lightparallelizing members 200 can convert direct light emitted by a linearlight source 125 to parallel light, by unifying the direction of lightusing, for example, light blocking members 210 as a broader term, suchas plate-shaped members 210 a of FIG. 8(b) or cylindrical members 210 bof FIG. 8(c), in a direction parallel to the axial line direction of thelinear light source 125 whose direction of light is random, among thedirect light emitted by the linear light source 125.

More specifically, among the direct light emitted by the linear lightsource 125, light with low parallelism with respect to the lightblocking members 210 such as plate-shaped members 210 a or cylindricalmembers 210 b, is brought into contact with these light blocking membersand is absorbed.

Therefore, only light with high parallelism, that is, parallel light,with respect to the light blocking members 210 such as plate-shapedmembers 210 a or cylindrical members 210 b can pass through theirradiated light parallelizing members 200, and as a result, the directlight emitted by the linear light source 125 is converted to parallellight by the irradiated light parallelizing members 200.

Meanwhile, the material for the light blocking members 210 such asplate-shaped members 210 a or cylindrical members 210 b is notparticularly limited as long as the material can absorb light with lowparallelism with respect to the light blocking members 210, and forexample, a heat resistant black-painted ulster steel sheet can be used.

It is also preferable that the parallelism of the irradiated light isadjusted to a value of 10° or less.

The reason for this is that when the parallelism of the irradiated lightis adjusted to a value within such a range, a columnar structure regionin which plural pillar-shaped objects are arranged to stand closetogether at a constant angle of inclination with respect to the filmthickness direction, can be formed efficiently and stably.

Therefore, it is more preferable that the parallelism of the irradiatedlight is adjusted to a value of 5° or less, and even more preferably toa value of 2° or less.

Furthermore, regarding the angle of irradiation of the irradiated light,it is preferable that the angle of irradiation θ3 as shown in FIG. 9, inthe case in which the angle of the normal line with respect to thesurface of the coating layer 1 is designated as 0°, is adjusted to avalue within the range of usually −80° to 80°.

The reason for this is that when the angle of irradiation has a valueother than the range of −80° to 80°, the influence of reflection or thelike at the surface of the coating layer 1 is increased, and it may bedifficult to form a sufficient columnar structure region.

Meanwhile, the arrow B in FIG. 9 indicates the traveling direction ofthe coating layer.

Furthermore, examples of the irradiated light include ultravioletradiation or an electron beam; however, it is preferable to useultraviolet radiation.

The reason for this is that, in the case of an electron beam, since thepolymerization rate is very fast, the component (A) and the component(B) may not undergo phase separation sufficiently during the course ofpolymerization, and it may be difficult to form a columnar structure. Onthe other hand, it is because when compared with visible light or thelike, ultraviolet radiation is associated with a wide variety ofultraviolet-curable resins that are cured by irradiation of ultravioletradiation, or a wide variety of photopolymerization initiators that canbe used, and therefore, the widths of selection of the component (A) andthe component (B) can be broadened.

Furthermore, regarding the conditions for irradiation of first activeenergy radiation, it is preferable that the peak illuminance at thecoating layer surface is adjusted to a value within the range of 0.1 to3 mW/cm².

The reason for this is that, if such a peak illuminance has a value ofbelow 0.1 mW/cm², a columnar structure-unformed region can be securedsufficiently; however, it may be difficult to form the first columnarstructure region in a well-defined manner. On the other hand, it isbecause, if such a peak illuminance has a value of above 3 mW/cm², eventhough a column structure-unformed region exists, it is speculated thatthe curing reaction proceeds excessively in the relevant region, and itmay be difficult to form the second columnar structure regionsufficiently in the second active energy ray irradiation step that willbe described below.

Therefore, it is more preferable that the peak illuminance at thecoating layer surface during the first active energy ray irradiation isadjusted to a value within the range of 0.3 to 2 mW/cm², and even morepreferably to a value within the range of 0.5 to 1.5 mW/cm².

Furthermore, it is preferable that the cumulative amount of light at thecoating layer surface for the first active energy ray irradiation isadjusted to a value within the range of 5 to 100 mJ/cm².

The reason for this is that, if such a cumulative amount of light has avalue of below 5 mJ/cm², it may be difficult to extend the firstcolumnar structure region sufficiently from the upper part toward thelower part, or the first columnar structure region may be deformed whenthe second columnar structure region is formed. On the other hand, it isbecause if such a cumulative amount of light has a value of above 100mJ/cm², curing of the columnar structure-unformed region proceedsexcessively, and in the second active energy ray irradiation step thatwill be described below, it may be difficult to form the second columnarstructure region sufficiently.

Therefore, it is more preferable that the cumulative amount of light atthe coating layer surface in the first active energy ray irradiation isadjusted to a value within the range of 7 to 50 mJ/cm², and even morepreferably to a value within the range of 10 to 30 mJ/cm².

Furthermore, it is preferable that at the time of the first activeenergy ray irradiation, the coating layer formed on the process sheet ismoved at a speed of 0.1 to 10 m/min.

The reason for this is that, if such a speed has a value of below 0.1m/min, mass productivity may be excessively decreased. On the otherhand, if such a speed has a value of above 10 m/min, the travel speedmay be faster than the speed of curing of the coating layer, in otherwords, the speed of formation of the columnar structure region, theincident angle of ultraviolet radiation to the coating layer may change,and the formation of the columnar structure region may be achievedinsufficiently.

Therefore, it is more preferable that, at the time of the first activeenergy ray irradiation, the coating layer formed on the process sheet ismoved at a speed within the range of 0.2 to 5 m/min, and is even morepreferably moved at a speed within the range of 0.3 to 3 m/min.

Furthermore, it is preferable from the viewpoint of efficiently leavinga columnar structure-unformed region, the first active energy rayirradiation step is carried out in an atmosphere containing oxygen(preferably, in an air atmosphere).

The reason for this is that when the first active energy ray irradiationis carried out in an atmosphere containing oxygen, while the firstcolumnar structure region can be formed efficiently in the lower portionof the coating layer, a columnar structure-unformed region can be leftstably in the upper portion of the coating layer by utilizing theinfluence of oxygen inhibition.

Therefore, in the second active energy ray irradiation that will bedescribed below, a second columnar structure-unformed region can be leftefficiently in such a columnar structure-unformed region.

That is, it is because, if the first active energy ray irradiation iscarried out not in an atmosphere containing oxygen but in a non-oxygenatmosphere that does not contain oxygen, the first columnar structureregion may be formed continuously, almost to the outermost surface ofthe film, without leaving a columnar structure-unformed region in theupper part of the film.

Meanwhile, the term “in an atmosphere containing oxygen” meansconditions in which the surface of the coating layer is in directcontact with a gas containing oxygen such as air, and among others, theterm “in an air atmosphere” means conditions in which the surface of thecoating layer is in direct contact with air.

Therefore, performing the first active energy ray irradiation in a statethat the surface of the coating layer is exposed directly to air withoutlaminating a film on the surface of the coating layer or performing aparticular means such as performing nitrogen purge, corresponds to thefirst active energy ray irradiation “in an air atmosphere”.

4. Step (d): Second Active Energy Ray Irradiation Step

Step (d) is, as illustrated in FIG. 7(c), a step of forming a secondcolumnar structure region 30 in the columnar structure-unformed region20′ by further subjecting the coating layer 1 to second active energyray irradiation.

Such a second active energy ray irradiation step can be basicallycarried out similarly to the first active energy ray irradiation step.

Furthermore, regarding the conditions for irradiation of the secondactive energy radiation, it is preferable that the peak illuminance atthe coating layer surface is adjusted to a value within the range of 0.1to 20 mW/cm².

The reason for this is that, if such a peak illuminance has a value ofbelow 0.1 mW/cm², it may be difficult to form the second columnarstructure region in a well-defined manner. On the other hand, it isbecause if such an illuminance has a value of above 20 mW/cm², it isspeculated that the curing speed becomes excessively fast, and thesecond columnar structure region may not be formed effectively.

Therefore, it is more preferable that the peak illuminance ofultraviolet radiation at the coating layer surface is adjusted to avalue within the range of 0.3 to 10 mW/cm², and even more preferably toa value within the range of 0.5 to 5 mW/cm².

Furthermore, it is preferable that the cumulative amount of light at thecoating layer surface during the second active energy ray irradiationhas a value within the range of 5 to 300 mJ/cm².

The reason for this is that, if such a cumulative amount of light has avalue of below 5 mJ/cm², it may be difficult to extend the secondcolumnar structure region sufficiently from the upper part toward thelower part. On the other hand, it is because if such a cumulative amountof light has a value of above 300 mJ/cm², the resulting film may undergocoloration.

Therefore, it is more preferable that the cumulative amount of light atthe coating layer surface is adjusted to a value within the range of 30to 200 mJ/cm², and even more preferably to a value within the range of50 to 150 mJ/cm².

Furthermore, it is preferable that the second active energy rayirradiation is carried out in a non-oxygen atmosphere.

The reason for this is that when the second active energy rayirradiation is carried out in a non-oxygen atmosphere, the secondcolumnar structure region can be formed efficiently by suppressing theinfluence of oxygen inhibition in the columnar structure-unformed regionobtained by the first active energy ray irradiation.

That is, it is because if the second active energy ray irradiation iscarried out not in a non-oxygen atmosphere but in an oxygen atmosphere,when the composition is irradiated at a high illuminance, the secondcolumnar structure region may be formed at a very shallow position nearthe surface; however, a difference in refractive index that is necessaryfor light diffusion may not be obtained. Furthermore, it is because whenthe composition is irradiated at a low illuminance, the second columnarstructure region may not be formed in the columnar structure-unformedregion under the influence of oxygen inhibition.

Meanwhile, the term “in a non-oxygen atmosphere” means the conditions inwhich the surface of the coating layer is not in direct contact with anoxygen atmosphere, or an atmosphere containing oxygen.

Therefore, for example, performing the second active energy rayirradiation in a state in which the surface of the coating layer islaminated with a film, or in a state in which nitrogen purging has beenperformed by replacing air with nitrogen gas, corresponds to the secondactive energy ray irradiation “in a non-oxygen atmosphere”.

Furthermore, regarding the second active energy ray irradiation “in anon-oxygen atmosphere” described above, it is particularly preferable toperform second active energy ray irradiation in a state of having anactive energy radiation transmitting sheet laminated on the surface ofthe coating layer.

The reason for this is that, by performing the second active energy rayirradiation as such, the influence of oxygen inhibition can besuppressed effectively, and the second columnar structure region can beformed more efficiently in the columnar structure-unformed region.

That is, when an active energy ray transmitting sheet is laminated onthe surface of the coating layer, an active energy radiation can beeffectively irradiated to the coating layer by causing the sheet totransmit the radiation, while stably preventing the surface of thecoating layer from being brought into contact with oxygen.

Meanwhile, regarding the active energy radiation transmitting sheet, anysheet capable of transmitting active energy radiation among the processsheets described in connection with step (b) (application step) can beused without any particular limitations.

Meanwhile, it is also preferable to further irradiate active energyradiation apart from the first and second active energy ray irradiation,so as to obtain a cumulative amount of light that allows sufficientcuring of the coating layer.

Since the active energy radiation used at this time is intended tosufficiently cure the coating layer, it is preferable to use notparallel light, but a light which is random in any direction ofpropagation between the longitudinal direction and the width directionof the film.

Also, the light diffusion film after the photocuring step is finallybrought into a state of being usable, by detaching the process sheet.

As described above, according to the present invention, since the firstcolumnar structure region and the second columnar structure region arerespectively formed by the first active energy ray irradiation and thesecond active energy ray irradiation, the combination of the angles ofinclination of the pillar-shaped objects in the respective columnarstructure regions can be regulated easily.

That is, the combination of the angles of inclination of thepillar-shaped objects in the various columnar structure regions can beregulated easily by simply appropriately regulating the angle ofirradiation for each of the active energy ray irradiations.

EXAMPLES

Hereinafter, the light diffusion film of the present invention and thelike will be explained in more detail by way of Examples.

Example 1

1. Synthesis of Component (B)

In a container, 2 moles of isophorone diisocyanate (IPDI) as a component(B1) and 2 moles of 2-hydroxyethyl methacrylate (HEMA) as a component(B3) were introduced with respect to 1 mole of polypropylene glycol(PPG) having a weight average molecular weight of 9,200 as a component(B2), and then the compounds were reacted according to a conventionalmethod. Thus, a polyether urethane methacrylate having a weight averagemolecular weight of 9,900 was obtained.

Meanwhile, the weight average molecular weights of polypropylene glycoland polyether urethane methacrylate are values calculated relative topolystyrene standards measured by gel permeation chromatography (GPC)under the following conditions:

GPC analyzer: manufactured by Tosoh Corp., HLC-8020

GPC column: manufactured by Tosoh Corp. (hereinafter, described in orderof passage)

-   -   TSK GUARD COLUMN HXL-H    -   TSK GEL GMHXL (x2)    -   TSK GEL G2000HXL

Measurement solvent: Tetrahydrofuran

Measurement temperature: 40° C.

2. Preparation of Composition for Light Diffusion Film

Subsequently, a composition for light diffusion film was obtained bymixing 100 parts by weight of a polyether urethane methacrylate having aweight average molecular weight of 9,900 as the component (B) thusobtained, with 100 parts by weight of o-phenylphenoxy ethoxyethylacrylate (manufactured by Shin Nakamura Chemical Co., Ltd., NK ESTERA-LEN-10) represented by the following Formula (3) and having amolecular weight of 268 as component (A), and 8 parts by weight of2-hydroxy-2-methyl-1-phenylpropan-1-one as component (C), and thenheating and mixing the mixture under the conditions of 80° C.

Meanwhile, the refractive indices of the component (A) and the component(B) were measured according to JIS K0062 using an Abbe refractometer(manufactured by Atago Co., Ltd., ABBE REFRACTOMETER DR-M2, Na lightsource, wavelength: 589 nm), and the refractive indices were 1.58 and1.46, respectively.

3. Application of Composition for Light Diffusion Film

Subsequently, the composition for light diffusion film thus obtained wasapplied on a film-like transparent polyethylene terephthalate(hereinafter, referred to as PET) as a process sheet, and thus a coatinglayer having a film thickness of 105 μm was obtained.

4. First Ultraviolet Irradiation

Subsequently, the coating layer was irradiated with parallel lighthaving a parallelism of 2° or less such that the angle of irradiation(θ3 in FIG. 9) would be almost 0°, using an ultraviolet spot parallellight source (Japan Technology System Corp.) having the central rayparallelism controlled to ±3° or less.

The peak illuminance at that time was set to 0.98 mW/cm², the cumulativeamount of light was set to 19.78 mJ/cm², the lamp height was set to 240mm, and the travel speed of the coating layer was set to 0.17 m/min.

5. Second Ultraviolet Irradiation

Subsequently, after the first ultraviolet irradiation step was carriedout, the exposed surface side of the coating layer was laminated with anultraviolet transmissive peeling film having a thickness of 38 μm(manufactured by Lintec Corp., SP-PET382050), and the laminate wasbrought into a state in a non-oxygen atmosphere.

Subsequently, similarly to the first ultraviolet irradiation step, thecoating layer was irradiated with parallel light through the peelingfilm such that the angle of irradiation (θ3 in FIG. 9) would be almost0°, and thus a light diffusion film having a film thickness of 105 μmwas obtained.

The peak illuminance at that time was set to 2.88 mW/cm², the cumulativeamount of light was set to 20.06 mJ/cm², the lamp height was set to 240mm, and the travel speed of the coating layer was set to 0.54 m/min.

Meanwhile, the film thickness of the light diffusion film was measuredusing a constant pressure thickness meter (manufactured by Takara Co.,Ltd., TECLOCK PG-02J).

Furthermore, it was confirmed that, as illustrated in the schematicdiagram of a film cross-section in FIG. 10(a), the light diffusion filmthus obtained was a light diffusion film which had a first columnarstructure region formed in the lower part of the film and a secondcolumnar structure region formed in the upper part of the film, and hadan overlapping columnar structure region formed by these columnarstructure regions partially overlapping.

Meanwhile, FIG. 10(a) is a schematic diagram of a cross-section obtainedin a case in which the film was cut at a plane that was parallel to thetravel direction of the coating layer and was perpendicular to the filmplane.

Furthermore, the film thickness of the first columnar structure regionwas 55 μm, the film thickness of the second columnar structure regionwas 60 μm, and the film thickness of the overlapping columnar structureregion was 10 μm.

Furthermore, the angle of inclination of the pillar-shaped objects inthe first columnar structure region, that is, the angle of inclinationof the pillar-shaped objects when the angle of the normal line to thefilm surface, which was measured at a cross-section in a case in whichthe film was cut by a plane that cuts one whole pillar-shaped objectinto two along the axial line, was designated as 0° (θa=θb in FIG. 6),was 0°. The angle of inclination of the pillar-shaped objects in thesecond columnar structure region measured at the same cross-section(θa′=θb′ in FIG. 6) was also 0°.

Furthermore, a cross-sectional photograph of the light diffusion filmthus obtained is shown in FIG. 10(b). FIG. 10(b) is a cross-sectionalphotograph obtainable in a case in which the film was cut at a planethat was parallel to the travel direction of the coating layer and wasperpendicular to the film plane.

6. Evaluation

Light was caused to enter the light diffusion film thus obtained, asillustrated in FIG. 10(a), through the lower side of the relevant film,that is, through the side where the first columnar structure regionexisted, while the incident angle θ1 (°) was varied to 40°, 35°, 30°,25°, 20°, 15°, 10°, 5°, 0°, −5°, −10°, −15°, −20°, −25°, −30°, −35°, and−40°, using a conoscope (manufactured by Autronic-Melchers GmbH).

Photographs of the diffusion state of the diffused light at each of theincident angles θ1 were taken in the Z-direction as shown in FIG. 10(a).Photographs of the cases in which the incident angle θ1 was 40° to −40°are presented in FIGS. 11(a) to 11(q), respectively.

From such results, it is understood that when the first and secondcolumnar structure regions are formed, despite being a thin film havinga thickness of 105 μm, straight transmission of incident light can beprevented even if the incident angle θ1 of incident light is 0°, andthus uniform light diffusion characteristics are sufficiently obtained.

Example 2

In Example 2, a light diffusion film having a film thickness of 142 μmwas obtained in the same manner as in Example 1, except that in regardto the step of applying the composition for light diffusion film, thefilm thickness of the coating layer was changed to 142 μm, and in regardto the second ultraviolet irradiation step, the angle of irradiation ofparallel light (θ3 in FIG. 9) was changed to 30°, the peak illuminancewas changed to 2.75 mW/cm², and the cumulative amount of light waschanged to 19.50 mJ/cm².

Furthermore, it was confirmed that the light diffusion film thusobtained was a light diffusion film in which, as illustrated in theschematic diagram of a film cross-section of FIG. 12(a), a firstcolumnar structure region was formed in the lower part of the film and asecond columnar structure region was formed in the upper part of thefilm.

Meanwhile, FIG. 12(a) is a schematic diagram of a cross-sectionobtainable in a case in which the film was cut at a plane that wasparallel to the travel direction of the coating layer and wasperpendicular to the film plane.

Furthermore, the film thickness of the first columnar structure regionwas 82 μm, the film thickness of the second columnar structure regionwas 72 μm, and the film thickness of the overlapping columnar structurewas 12 μm.

Furthermore, the angle of inclination of the pillar-shaped objects inthe first columnar structure region (θa=θb in FIG. 6) was 0°, and theangle of inclination of the pillar-shaped objects in the second columnarstructure region measured at the same cross-section (θa′=θb′ in FIG. 6)was 30°.

Furthermore, a cross-sectional photograph of the light diffusion filmthus obtained is presented in FIG. 12(b). FIG. 12(b) is across-sectional photograph obtainable in the case in which the film wascut at a plane that was parallel to the travel direction of the coatinglayer and was perpendicular to the film plane.

Furthermore, the diffusion state of diffused light in the case in whichthe incident angle θ1 was changed in the same manner as in Example 1.

That is, as illustrated in FIG. 12(a), light was caused to enter thelight diffusion film thus obtained, through the lower part of therelevant film, while the incident angle θ1 (°) was varied to 40°, 35°,30°, 25°, 20°, 15°, 10°, 5°, 0°, −5°, −10°, −15°, −20°, −25°, −30°,−35°, −40°, −45°, −50°, −55°, −60°, and −65°.

Then, photographs of the diffusion state of the diffused light at eachof the incident angles θ1 were taken in the Z-direction of FIG. 12(a).Photographs of the cases in which the incident angle θ1 was 40° to −65°are presented in FIGS. 13(a) to 13(v), respectively.

From such results, it is understood that the light diffusion filmexhibits isotropic light diffusion characteristics according to theangle of inclination of the pillar-shaped objects in the first andsecond columnar structure regions, respectively, or isotropic lightdiffusion characteristics that have been complexed by passing throughtwo columnar structure regions, at a wide range of incident angles ofincident light.

Example 3

In Example 3, in regard to the step of applying the composition forlight diffusion film, the film thickness of the coating layer waschanged to 142 μm, and in regard to the first ultraviolet irradiationstep, the angle of irradiation of parallel light (θ3 in FIG. 9) waschanged to 30°, the peak illuminance was changed to 1.05 mW/cm², thecumulative amount of light was changed to 20.88 mJ/cm², and the travelspeed of the coating layer was changed to 0.17 m/min.

Furthermore, in regard to the second ultraviolet irradiation step, theangle of irradiation of parallel light (θ3 in FIG. 9) was changed to−30°, the peak illuminance was changed to 2.75 mW/cm², and thecumulative amount of light was changed to 19.50 mJ/cm².

Other than that, a light diffusion film having a film thickness of 142μm was obtained in the same manner as in Example 1.

Furthermore, it was confirmed that the light diffusion film thusobtained was a light diffusion in which, as illustrated in the schematicdiagram of the film cross-section of FIG. 14(a), a first columnarstructure region was formed in the lower part of the film, and a secondcolumnar structure region was formed in the upper part of the film.

Meanwhile, FIG. 14(a) is a schematic diagram of a cross-sectionobtainable when the film was cut at a plane that was parallel to thetravel direction of the coating layer and was perpendicular to the filmsurface.

Furthermore, the film thickness of the first columnar structure regionwas 82 μm, the film thickness of the second columnar structure regionwas 66 μm, and the film thickness of the overlapping columnar structureregion was 6 μm.

Furthermore, the angle of inclination of the pillar-shaped objects inthe first columnar structure region (θa=θb in FIG. 6) was 30°, and theangle of inclination of the pillar-shaped objects in the second columnarstructure region measured at the same cross-section (θa′=θb′ in FIG. 6)was 30°

Furthermore, a cross-sectional photograph of the light diffusion filmthus obtained is presented in FIG. 14(b). FIG. 14(b) is across-sectional photograph obtained in the case in which the film wascut at a plane that is parallel to the travel direction of the coatinglayer and is perpendicular to the film plane.

Furthermore, the diffusion state of diffused light in the case ofvarying the incident angle θ1 was evaluated in the same manner as inExample 1.

That is, as illustrated in FIG. 14(a), light was caused to enter thelight diffusion film thus obtained, through the lower part of therelevant film, while the incident angle θ1 (°) was varied to 60°, 55°,50°, 45°, 40°, 35°, 30°, 25°, 20°, 15°, 10°, 5°, 0°, −5°, −10°, −15°,−20°, −25°, −30°, −35°, −40°, −45°, −50°, and −55°.

Furthermore, photographs of the diffusion state of diffused light ateach of the incident angles θ1 were taken in the Z-direction in FIG.14(a). Photographs of the cases in which the incident angle θ1 was 60°to −55° are presented in FIGS. 15(a) to 15(x), respectively.

From such results, it is understood that the light diffusion filmexhibits isotropic light diffusion characteristics according to theangle of inclination of the pillar-shaped objects in the first andsecond columnar structure regions, respectively, or isotropic lightdiffusion characteristics that have been complexed by passing throughtwo columnar structure regions, at a wide range of incident angles ofincident light.

Comparative Example 1

In Comparative Example 1, in regard to the second ultravioletirradiation step, scattered light at a peak illuminance of 10.2 mW/cm²and a cumulative amount of light of 142.2 mJ/cm² was irradiated, and thetravel speed of the coating layer was changed to 0.40 m/min.

Other than that, a light diffusion film having a film thickness of 152μm was obtained in the same manner as in Example 1.

Furthermore, it was confirmed that, as illustrated in the schematicdiagram of the film cross-section of FIG. 16(a), the light diffusionfilm thus obtained was a light diffusion film in which a first columnarstructure region was formed in the lower part of the film, and a secondcolumnar structure region was not formed in the upper part of the film.

Meanwhile, FIG. 16(a) is a schematic diagram of a cross-sectionobtainable when the film was cut at a plane that was parallel to thetravel direction of the coating layer and was perpendicular to the filmplane.

Furthermore, the film thickness of the first columnar structure regionwas 86 μm, and the angle of inclination of the pillar-shaped objects inthe first columnar structure region (θa=θb in FIG. 6) was 0°.

Furthermore, a cross-sectional photograph of the light diffusion filmthus obtained is presented in FIG. 16(b). FIG. 16(b) is across-sectional photograph in the case in which the film was cut at aplane that was parallel to the travel direction of the coating layer andwas perpendicular to the film plane.

Furthermore, the diffusion state of diffused light in the case in whichthe incident light θ1 was changed was evaluated in the same manner as inExample 1.

That is, as illustrated in FIG. 16(a), light was caused to enter thelight diffusion film thus obtained, through the lower part of therelevant film, while the incident angle θ1 (°) was varied to 40°, 35°,30°, 25°, 20°, 15°, 10°, 5°, 0°, −5°, −10°, −15°, −20°, −25°, −30°,−35°, and −40°.

Then, photographs of the diffusion state of diffused light at each ofthe incident angles θ1 were taken in the Z-direction in FIG. 16(a).Photographs of the cases in which the incident angle θ1 was 40° to −40°are presented in FIGS. 17(a) to 17(q), respectively.

From such results, it is understood that when compared with Example 1,despite that the total film thickness was thicker than that of the lightdiffusion film of Example 1, sufficiently uniform light diffusioncharacteristics were not obtained because the film thickness of thecolumnar structure region was thin, as can be seen from the results ofan observation of the cross-section.

Particularly, it is understood that when the incident angle θ1 ofincident light is 0°, straight transmission of incident light may not beprevented, and the light diffusion characteristics become markedlynon-uniform.

Comparative Example 2

In Comparative Example 2, in regard to the step of applying thecomposition for light diffusion film, the film thickness of the coatinglayer was changed to 138 μm, and in regard to the first ultravioletirradiation step, the angle of irradiation of parallel light (θ3 in FIG.9) was changed to 30°, the peak illuminance was changed to 2.75 mW/cm²,the cumulative amount of light was changed to 19.50 mJ/cm², and thetravel speed of the coating layer was changed to 0.54 m/min.

Furthermore, in regard to the second ultraviolet irradiation step,scattered light at a peak illuminance of 10.2 mW/cm² and a cumulativeamount of light of 142.2 mJ/cm² was irradiated, and also, the travelspeed of the coating layer was changed to 0.40 m/min.

Other than that, a light diffusion film having a film thickness of 138μm was obtained in the same manner as in Example 1.

Also, it was confirmed that, as illustrated in the schematic diagram ofthe film cross-section of FIG. 18(a), the light diffusion film thusobtained was a light diffusion film in which a first columnar structureregion was formed in the lower part of the film, and a second columnarstructure region was not formed in the upper part of the film.

Meanwhile, FIG. 18(a) is a schematic diagram of a cross-sectionobtainable when the film was cut at a plane that was parallel to thetravel direction of the coating layer and was perpendicular to the filmplane.

Furthermore, the film thickness of the first columnar structure regionwas 104 μm, and the angle of inclination of the pillar-shaped objects inthe first columnar structure region (θa=θb in FIG. 6) was 30°.

Furthermore, a cross-sectional photograph of the light diffusion filmthus obtained is presented in FIG. 18(b). FIG. 18(b) is across-sectional photograph in the case in which the film was cut at aplane that was parallel to the travel direction of the coating layer andwas perpendicular to the film plane.

Furthermore, the diffusion state of diffused light in the case in whichthe incident light θ1 was changed was evaluated in the same manner as inExample 1.

That is, as illustrated in FIG. 18(a), light was caused to enter thelight diffusion film thus obtained, through the lower part of therelevant film, while the incident angle θ1 (°) was varied to 10°, 5°,0°, −50, −10°, −15°, −20°, −25°, −30°, −35°, −40°, −45°, −50°, −55°,−60°, and −65°.

Then, photographs of the diffusion state of diffused light at each ofthe incident angles θ1 were taken in the Z-direction in FIG. 18(a).Photographs of the cases in which the incident angle θ1 was 10° to −65°are presented in FIGS. 19(a) to 19(p), respectively.

From such results, it is understood that when compared with Example 3,since the first ultraviolet irradiation was performed at a higherilluminance than in the case of Example 3, the film thickness of thefirst columnar structure region was thicker, and the uniformity ofisotropic light diffusion in the first columnar structure region alonewas high; however, in a wide range of the incident angle of incidentlight, light diffusion characteristics may not be sufficientlymanifested.

INDUSTRIAL APPLICABILITY

As discussed above, according to the present invention, the uniformityof the intensity of diffused light in the light diffusion angle regioncan be increased, or the light diffusion angle region can be expandedeffectively, by forming a first columnar structure region and a secondcolumnar structure region in a same film.

Therefore, the light diffusion film or the like of the present inventioncan be supplied to a light control film for a reflective type liquidcrystal display devices, as well as a viewing angle control film, aviewing angle expansion film, and a screen for projection, and it isexpected that the light diffusion film can contribute markedly to anenhancement of the product quality of these devices.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1: Coating layer    -   2: Process sheet    -   10: Light diffusion film (isotropic light diffusion film)    -   12: Pillar-shaped object having a relatively high refractive        index    -   13: Columnar structure region    -   13′: Boundary surface of columnar structure    -   14: Region having a relatively low refractive index    -   20: First columnar structure region    -   20′: Columnar structure-unformed region    -   30: Second columnar structure region    -   40: Light diffusion film of the invention    -   50: Overlapping columnar structure region    -   60: Irradiated light from light source    -   70: Parallel light    -   125: Linear light source    -   200: Irradiated light parallelizing member    -   202: Point light source    -   204: Lens    -   210: Light blocking member    -   210 a: Plate-shaped member    -   210 b: Cylindrical member

The invention claimed is:
 1. A light diffusion film comprising asingle-layered light diffusion layer including, sequentially from thelower part of the film along a film thickness direction, a firstcolumnar structure region and a second columnar structure region, inwhich plural pillar-shaped objects having a relatively high refractiveindex are arranged to stand close together in a region having arelatively low refractive index, the light diffusion film being aphotocured product of a composition for a light diffusion film, andwherein the light diffusion film comprises an overlapping columnarstructure region in which an upper end of the first columnar structureregion extends into a lower end of the second columnar structure regionso that the upper end of the first columnar structure region and thelower end of the second columnar structure region overlap with eachother in a cross-section of the light diffusion film when the lightdiffusion film is cut at a plane that is perpendicular to a lightdiffusion film plane and cuts the pillar-shaped objects into two alongaxial lines in the first columnar structure region and the secondcolumnar structure region.
 2. The light diffusion film according toclaim 1, wherein the overlapping columnar structure region is formed bytips of any one side of the pillar-shaped objects respectivelyoriginating from the first columnar structure region and the secondcolumnar structure region, being brought into contact with a vicinity ofthe tips of the pillar-shaped objects originating from the othercolumnar structure region.
 3. The light diffusion film according toclaim 1, wherein a thickness of the overlapping columnar structureregion is adjusted to a value within the range of 1 to 40 μm.
 4. Thelight diffusion film according to claim 1, wherein a thickness of theoverlapping columnar structure region is adjusted to a value within therange of 0.1% to 10% relative to a film thickness, taken as 100%.
 5. Thelight diffusion film according to claim 1, wherein in the overlappingcolumnar structure region, the absolute value of the difference betweenangles of inclination of the pillar-shaped objects respectivelyoriginating from the first columnar structure region and the secondcolumnar structure region is adjusted to a value of 1° or more.
 6. Thelight diffusion film according to claim 1, wherein a main component ofthe pillar-shaped objects in the first columnar structure region and thesecond columnar structure region is a (meth)acrylic acid ester polymercontaining plural aromatic rings, and a main component of the regionhaving a relatively low refractive index is a polymer of urethane(meth)acrylate.
 7. A method for manufacturing a light diffusion film,the method comprising the following steps (a) to (d): (a) a step ofpreparing a composition for light diffusion film; (b) a step of applyingthe composition for light diffusion film on a process sheet, and forminga coating layer; (c) a step of subjecting the coating layer to firstactive energy ray irradiation, and forming a first columnar structureregion in a lower portion of the coating layer, in which pluralpillar-shaped objects having a relatively high refractive index arearranged to stand close together in a region having a relatively lowrefractive index, while leaving a columnar structure-unformed region inan upper portion of the coating layer; and (d) a step of subjecting thecoating layer to second active energy ray irradiation, and forming asecond columnar structure region in the columnar structure-unformedregion, in which plural pillar-shaped objects having a relatively highrefractive index are arranged to stand close together in a region havinga relatively low refractive index, and wherein an upper end of the firstcolumnar structure region extends into a lower end of the secondcolumnar structure region so that the upper end of the first columnarstructure region and the lower end of the second columnar structureregion overlap with each other in a cross-section of the light diffusionfilm when the light diffusion film is cut at a plane that isperpendicular to a light diffusion film plane and cuts the pillar-shapedobjects into two along axial lines in the first columnar structureregion and the second columnar structure region.
 8. The method formanufacturing a light diffusion film according to claim 7, wherein thefirst active energy ray irradiation is performed in an oxygen-containingatmosphere, while the second active energy ray irradiation is performedin a non-oxygen atmosphere.
 9. A light diffusion film comprising asingle-layered light diffusion layer including, sequentially from alower part of the film along a film thickness direction, a firstcolumnar structure region and a second columnar structure region, inwhich plural pillar shaped objects having a relatively high refractiveindex are arranged to stand close together in a region having arelatively low refractive index, wherein the light diffusion filmcomprises an overlapping columnar structure region in which an upper endof the first columnar structure region extends into a lower end of thesecond columnar structure so that the upper end of the first columnarstructure region and the lower end of the second columnar structureregion overlap with each other in a cross-section of the light diffusionfilm when the light diffusion film is cut at a plane that isperpendicular to a light diffusion plane and cuts the pillar shapedobjects into two along axial lines in the first columnar structureregion and the second columnar structure region, a thickness of theoverlapping columnar structure region is adjusted to a value within therange of 0.1% to 10% relative to a film thickness, taken as 100%, and avalue obtained by subtracting the thickness of the overlapping columnarstructure region from the sum of the thickness of the first columnarstructure region and the second columnar structure region is adjusted toa value of 80% or more relative to the film thickness, taken as 100%.